In short

Most Greek adjectives follow the familiar -ος, -η/-α, -ο pattern. This lesson adds the three classes that a B1 learner meets constantly and that do not fit it: the quantifier πολύς “much, many”, the everyday -ύς / -ιά / -ύ type (βαθύς “deep”, βαρύς “heavy”), and the -ης / -ης / -ες type of Ancient origin (διεθνής “international”, ακριβής “exact”). Around them sit three small groups: the expressive -ης / -α / -ικο adjectives of character (ζηλιάρης “jealous”), the colour adjectives in -ής / -ιά / -ί (θαλασσής “sea-blue”) together with the fully indeclinable loans μπλε, ροζ, γκρι, and adjectives used as nouns (ο μικρός “the little one”, τα ελληνικά “Greek”).

The single biggest payoff is spelling: πολύ, πολλή and πολλά sound almost interchangeable to an English ear but are three different words on paper, and the genitive of διεθνής is διεθνούς, never *διεθνή.

The rule

1. πολύς is irregular and mixes two stems. The whole masculine and neuter singular uses the short stem πολ- (πολύς, πολύ — including the genitive, which is simply πολύ), while the feminine and the entire plural use a double λ: πολλή, πολλής, πολλοί, πολλές, πολλά. It agrees with its noun like any adjective, so the form you write is decided by the gender, number and case of the noun — not by the sound.

The same string πολύ is also the adverb “very / much / too” (μιλάει πολύ, πολύ ωραία). That adverb is invariable and never becomes *πολλή.

2. The -ύς / -ιά / -ύ type covers a small but very frequent set of physical-dimension adjectives: βαθύς, πλατύς, φαρδύς, μακρύς, βαρύς, παχύς, ελαφρύς. The masculine and the neuter nominative and accusative singular behave like a shortened -ος adjective; the feminine, the genitive singular and the whole plural are built on a -ι- stem: βαθιά, βαθιού, βαθιοί, βαθιές. Note that the neuter plural (βαθιά) is identical to the feminine singular (βαθιά) — context and the article tell them apart: τα βαθιά νερά vs η βαθιά θάλασσα.

3. The -ης / -ης / -ες type is a learned class that has settled into ordinary language. Masculine and feminine are identical in every cell except the vocative singular, where the masculine usually drops the -ς (διεθνή, although διεθνής is listed too) while the feminine always keeps it (διεθνής); only the neuter differs elsewhere. Its endings come from the Ancient third declension, which is why the genitive singular is -ούς (διεθνούς) and the plural nominative is -είς (διεθνείς) with a neuter in -ή (διεθνή). The stress never moves inside the paradigm: it stays on the ending in διεθνής, ακριβής, συνεχής, and on the stem in πλήρης (πλήρους, πλήρη, πλήρεις, πλήρων).

4. Three smaller groups. The -ης / -α / -ικο adjectives describe character or habit and take the “-ηδες” plural in the masculine (ζηλιάρηδες); they are expressive rather than substandard — the dictionary gives ζηλιάρης, τεμπέλης, γκρινιάρης no register label at all. The colour adjectives in -ής / -ιά / -ί decline like the -ύς type but with -ής in the masculine and -ί in the neuter, and that -ί form is also listed separately as an indeclinable adjective that can go with any noun. The imported colour words μπλε, ροζ, γκρι, μπεζ, μοβ, καφέ take no endings at all — one form for all genders, numbers and cases.

5. Substantivisation. Any adjective can drop its noun and stand alone with the article: ο μικρός “the little boy”, η μικρή “the little girl”, οι μεγάλοι “the grown-ups”, τα γλυκά “the sweets”. Language names are the neuter plural: τα ελληνικά, τα αγγλικά, τα γαλλικά — and after μιλάω the article is usually dropped: μιλάω ελληνικά.

Forms & patterns

πολύς, πολλή, πολύ — “much, many, a lot of”

A quantifier is never used to call somebody, so πολύς has no vocative in practice. The masculine and neuter genitive singular is avoided as well: the form actually listed is the uninflected πολύ, with πολλού only as a secondary variant, and in speech people simply rephrase (πολλή δουλειά, από πολλή δουλειά). The genitive plural πολλών, by contrast, is everyday: η γνώμη πολλών ανθρώπων.

βαθύς, βαθιά, βαθύ — “deep”

Two sets of variants sit beside these forms and are listed in the dictionary, so you will meet them: an uninflected masculine and neuter genitive singular βαθύ next to βαθιού, and the learned masculine plural βαθείς and genitive plural βαθέων next to βαθιοί, βαθιών (παχύς likewise has a learned genitive παχέος). The -ι- forms are the normal spoken ones.

Same pattern, high-frequency members:

Two of these feminines double as very common adverbs: μακριά “far away” (μένω μακριά) and βαριά “heavily” (ανασαίνει βαριά). The adjective and the adverb are spelled the same.

διεθνής, διεθνής, διεθνές — “international”

Same pattern, high-frequency members:

The adverbs of this class usually end in -ώς: ακριβώς “exactly”, διεθνώς “internationally”, συνεχώς “continuously”. It is not automatic, though. For ειλικρινής the everyday adverb is ειλικρινά and ειλικρινώς is the learned variant; υγιώς is likewise marked as learned; and συνεχής has a second, plain adverb συνέχεια “all the time” beside συνεχώς.

ζηλιάρης, ζηλιάρα, ζηλιάρικο — adjectives of character

The feminine has no genitive plural in use (a form *ζηλιάρων is not said); rephrase with the masculine or with an ordinary -η adjective instead.

Like it: τεμπέλης / τεμπέλα / τεμπέλικο “lazy”, γκρινιάρης / γκρινιάρα / γκρινιάρικο “grumbling”, πεισματάρης / πεισματάρα / πεισματάρικο “stubborn”, κλαψιάρης / κλαψιάρα / κλαψιάρικο “whiny”. They are warm and vivid, but they are not slang: the dictionary marks none of them as familiar or popular, and they turn up in ordinary writing as well as in speech. Watch out for κατσούφης “sullen”, which looks like one of them but is a noun (ο κατσούφης, η κατσούφα); its adjective is the regular κατσούφικος, κατσούφικη, κατσούφικο, and that one is marked as familiar.

θαλασσής, θαλασσιά, θαλασσί — colours; and the indeclinable loans

Like it: σταχτής / σταχτιά / σταχτί “ash-grey”, καφετής / καφετιά / καφετί “brown”, πορτοκαλής / πορτοκαλιά / πορτοκαλί “orange”. The -ί form is the one you hear most, and not only with neuter nouns: θαλασσί, σταχτί, πορτοκαλί, καφετί are each listed a second time as fully indeclinable adjectives, so μια πορτοκαλί τσάντα and μια θαλασσί κουρτίνα are as correct as μια πορτοκαλιά τσάντα and μια θαλασσιά κουρτίνα — and ένα σταχτί παλτό is of course right too.

The borrowed colours never change:

Also invariable: μπεζ, μοβ, καφέ, λιλά, τιρκουάζ. The monosyllabic ones take no accent at all (μπλε, ροζ, γκρι, μπεζ, μοβ); the longer ones carry their accent like any other word (καφέ, λιλά, τιρκουάζ) — but the accent never moves, because the form never changes.

Adjectives used as nouns

Examples

Common mistakes

• Έχω πολύ δουλειά. -> Έχω πολλή δουλειά. — δουλειά is feminine, so the feminine form πολλή (two λ, ending -ή) is required; πολύ is neuter or adverb.
• Είδα πολύ πράγματα. -> Είδα πολλά πράγματα. — with a plural noun you need the plural πολλά; πολύ can only mean “very / much”.
• Ήρθαν πολύ άνθρωποι. -> Ήρθαν πολλοί άνθρωποι. — masculine plural takes πολλοί.
• Είναι πολλή ωραία. -> Είναι πολύ ωραία. — here the word modifies an adverb/adjective, so it is the invariable adverb πολύ, never πολλή.
• βαθής θάλασσα -> βαθιά θάλασσα — the -ύς type has no feminine in -ής; the feminine is -ιά.
• βαθειά, βαρειά -> βαθιά, βαριά — the demotic spelling of this feminine is plain -ιά, with no ε.
• του βαθύς ποταμού -> του βαθιού ποταμού — the everyday genitive singular is built on the -ι- stem; the uninflected του βαθύ ποταμού is also listed, but the nominative form is never used after the article.
• του διεθνή οργανισμού -> του διεθνούς οργανισμού — διεθνή is the accusative singular; the genitive is διεθνούς.
• το διεθνή αεροδρόμιο -> το διεθνές αεροδρόμιο — with a neuter noun the ending is -ές.
• οι συνεχής προσπάθειες -> οι συνεχείς προσπάθειες — the plural of -ης is -είς for both masculine and feminine.
• μια ακριβής ζωή (meaning “an expensive life”) -> μια ακριβή ζωή — ακριβής means “exact”; “expensive” is ακριβός, ακριβή, ακριβό.
• τα μπλα παπούτσια, ένα μπλέ πουκάμισο -> τα μπλε παπούτσια, ένα μπλε πουκάμισο — μπλε is indeclinable and unaccented; it never agrees.

Tips

• Say the noun first, then choose the form. Gender and number decide πολύς / πολλή / πολύ / πολλοί / πολλές / πολλά — never the sound of the phrase.
• A quick written test for πολύ vs πολλή/πολλά: if you can replace the word with “very” or “a lot” (no noun follows), write πολύ. If a noun follows, make it agree.
• Learn the -ύς type as a pair, masculine plus feminine: βαθύς–βαθιά, βαρύς–βαριά, φαρδύς–φαρδιά. Once the feminine is right, every oblique form follows from the -ι- stem.
• For the -ης / -ης / -ες class memorise a three-cell skeleton per word: nominative διεθνής, genitive διεθνούς, neuter διεθνές. Everything else is predictable from those.
• Watch the near-pairs that differ by one letter: ακριβής “exact” vs ακριβός “expensive”, πλήρης “full” vs its synonym γεμάτος, συνεχής (adjective) vs συνεχώς (adverb).
• Tell the two groups apart by feel, not by register: τεμπέλης and ζηλιάρης are vivid character words, while διεθνής, πλήρης and συνεχής are neutral adjectives of Ancient origin. Neither group is restricted — you will read ζηλιάρης in a newspaper, and πλήρης is plain everyday speech (το τρένο έφυγε πλήρες, όλες οι πτήσεις για τη Ρόδο ήταν πλήρεις).
• When a colour is borrowed (μπλε, ροζ, γκρι, μπεζ, μοβ), stop declining and relax — the article alone carries the agreement: ο μπλε, η μπλε, το μπλε, οι μπλε, τα μπλε.