In short

Greek builds new words in two ways. Derivation (παραγωγή) glues a prefix (πρόθημα) or a suffix (επίθημα) onto a stem: καθαρός -> καθαρίζω, κλειδώνω -> ξεκλειδώνω. Compounding (σύνθεση) welds two words together with a linking -ο-: χαρτί + πετσέτα -> χαρτοπετσέτα.

Three things make this worth a lesson of its own rather than a vocabulary list:

• The suffix decides the gender and the declension of the new noun. Once you know that -ση is feminine and -μα is neuter, you never learn those genders again.
• The new word gets one accent, and it is often not where either original word had it: ψάρι + σούπα -> ψαρόσουπα.
• A small set of suffixes is productive - native speakers coin with them daily (σκανάρω, ποστάρω, ταινιάρα). Most others are frozen, and inventing with them produces a non-word.

Augmentatives (μεγεθυντικά) in -άρα, -αράς, -αρος, -ούκλα are the “big / impressive” suffixes - -άρα and -αράς coin the most freely, -αρος and -ούκλα are rarer but still build new words from nouns - and they overwrite the base’s gender. Diminutives are the mirror image and belong to lesson 41.

The rule

Four parts. Analyse any Greek word as πρόθημα + θέμα + επίθημα + κατάληξη. The θέμα (stem) carries the lexical meaning, the κατάληξη (inflectional ending) carries case/person and changes as the word inflects, and the επίθημα (derivational suffix) sits between them and does not change: in ξε-κλειδ-ών-ω the -ω is what becomes -εις, -ει, while -ων- stays put right through the present (only the perfective stem replaces it: ξεκλείδωσα).

Suffixes assign a class. A derivational suffix does two jobs at once: it changes the meaning and it hands the word to a declension or conjugation. -ση always gives a feminine noun of the λύση class; -μα always gives a neuter of the μάθημα class (gen. του μαθήματος); -ποιώ always gives a contracted verb of the second conjugation (απλοποιώ, απλοποιείς). So the ending you choose fixes the whole paradigm.

Prefixes attach to finished words. ξε-, ξανα-, παρα- combine with a fully formed verb and do not change its conjugation: γράφω -> ξαναγράφω conjugates exactly like γράφω. The learned prefixes α-/αν-, υπερ-, συν-, δυσ-/ευ- are inherited but still productive; συν- assimilates to the following consonant (συν + μαθητής -> συμμαθητής, συν + κάτοικος -> συγκάτοικος).

Compounding uses -ο-. Strip the first word’s ending, add -ο-, then attach the second word: αλάτι + πιπέρι -> αλατοπίπερο. The first member loses its accent entirely; the compound keeps exactly one. Very often that accent retracts as far left as the three-syllable rule permits (ψαρόσουπα, αγριόγατα, ποδόσφαιρο), but plenty of compounds simply keep the second member’s own accent (χαρτοπετσέτα, μαυροπίνακας). There is no way to predict this from first principles - learn the compound as a word.

In verb + verb compounds only the second verb inflects; the first appears as a bare stem plus -ο-: ανοίγω + κλείνω -> ανοιγοκλείνω, μπαίνω + βγαίνω -> μπαινοβγαίνω, πηγαίνω + έρχομαι -> πηγαινοέρχομαι.

Phrasal compounds (πολυλεκτικά σύνθετα) set two nouns side by side with no linking vowel, written with a hyphen or simply as two words - dictionaries print them unhyphenated (λέξη κλειδί, θέση κλειδί, άνθρωπος κλειδί): λέξη-κλειδί, παιδί-θαύμα, εταιρεία-κολοσσός. Both nouns go to the plural, and the second stays in the nominative - it is an apposition, not a genitive: λέξεις-κλειδιά, παιδιά-θαύματα.

Acronyms (αρκτικόλεξα) are written in capitals, with no accents and (in current usage) no full stops. Their gender comes from the head noun of the full name: η ΔΕΗ (η επιχείρηση), τα ΚΤΕΛ (τα ταμεία), τα ΕΛΤΑ (τα ταχυδρομεία). They do not decline.

Augmentatives express large size, and just as often admiration or crudeness. -άρα is the workhorse and is always feminine, whatever the base was: το αμάξι -> η αμαξάρα, το βιβλίο -> η βιβλιάρα. -αράς makes a masculine person noun (with feminine -αρού): η κοιλιά -> ο κοιλαράς, η κοιλαρού. -αρος and -ούκλα are older and much less frequent, but they still derive from nouns: το παιδί -> ο παίδαρος, το κορίτσι -> ο κορίτσαρος, το χέρι -> η χερούκλα, το μάτι -> η ματούκλα. All of them are informal, spoken register.

Forms & patterns

Analysing a word

Productive noun suffixes

The -ση / -ξη / -ψη choice is not free: it copies the perfective stem. λύ-σ-ω -> λύση, πρά-ξ-ω -> πράξη, σκε-ψ- -> σκέψη.

Productive adjective suffixes

Productive verb suffixes

Prefixes

Compounding with -ο-

Phrasal compounds and acronyms

Augmentatives

A derived noun in -ση: η ενημέρωση

The accent moves right in the plural (ενημέρωση -> ενημερώσεις, των ενημερώσεων): these nouns are learned in origin, and in the plural the stress sits on the last syllable of the stem, immediately before the ending. Formal written Greek also has a genitive singular της ενημερώσεως - a learned form, treated in lesson 62.

An augmentative in -άρα: η αμαξάρα

Nouns in -άρα have no genitive plural in use - there is no *των αμαξάρων. They follow the πείνα class, which simply lacks that cell; rephrase instead (η τιμή στις αμαξάρες).

A compound noun: το χειρόγραφο (χέρι + γράφω)

Note the accent shifting right in the genitive: χειρόγραφο -> του χειρογράφου, των χειρογράφων.

A verb in -ώνω: ενημερώνω (ενεστώτας)

A verb in -ποιώ: απλοποιώ (ενεστώτας)

A compound verb: μπαινοβγαίνω (ενεστώτας)

Only βγαίνω inflects. In the imperfect the accent retracts: μπαινόβγαινα, μπαινόβγαινες, μπαινόβγαινε.

Examples

Common mistakes

• ξεγράφω την εργασία -> ξαναγράφω την εργασία - ξε- means “undo”, so ξεγράφω is “write off, cross out”; “again” is ξανα-.
• χαρτιπετσέτα -> χαρτοπετσέτα - the linking vowel of a compound is -ο-, no matter what ending the first word had.
• ψαροσούπα -> ψαρόσουπα - a compound keeps exactly one accent, and in this word it retracts to the third-from-last syllable.
• ανοίγω-κλείνω το παράθυρο -> ανοιγοκλείνω το παράθυρο - in a verb + verb compound only the second verb inflects; the first is a bare stem plus -ο-.
• ένα ξυλικό τραπέζι -> ένα ξύλινο τραπέζι - -ινος means “made of / belonging to”, while -ικός means “having to do with” (ιστορικός, παιδικός).
• καθαροποιώ το σπίτι -> καθαρίζω το σπίτι - -ποιώ is learned in origin and no longer coins everyday verbs: the new ones it makes are technical or official (ψηφιοποιώ, ιδιωτικοποιώ), so for an everyday action use the -ίζω verb that already exists. The established -ποιώ verbs are themselves ordinary words, not formal ones: τακτοποιώ τα ρούχα μου is plain spoken Greek.
• το αμαξάρα -> η αμαξάρα - the augmentative suffix, not the base word, sets the gender: -άρα is feminine even from neuter το αμάξι.
• Το χειρόγραφο του χάθηκε. -> Το χειρόγραφό του χάθηκε. - a word stressed on its third-from-last syllable takes a second accent when a weak pronoun follows.
• η Δεη μάς έστειλε λογαριασμό -> η ΔΕΗ μάς έστειλε λογαριασμό - acronyms stay in capitals and carry no accent.

Tips

• The suffix gives you the gender for free: -ση/-ξη/-ψη, -ότητα, -ιά, -άρα are feminine; -μα, -είο, -τήριο, -άδικο are neuter; -τής is masculine with -τρια beside it. Learn the suffix once instead of each word’s gender.
• To pick between -ση, -ξη and -ψη, look at the perfective stem: λύ-σ-ω -> λύση, πρά-ξ-ω -> πράξη, σκε-ψ- -> σκέψη.
• The three “place” suffixes differ in register, not meaning: -είο is neutral (φαρμακείο, βιβλιοπωλείο), -τήριο is functional (γυμναστήριο, καθαριστήριο), -άδικο/-ίδικο is colloquial (ψαράδικο, σουβλατζίδικο).
• -άρω is the door loanwords come in through, with an aorist in -αρα (παρκάρω -> πάρκαρα, σκανάρω -> σκάναρα). Use it for genuine loans, not to dress up a word you invented.
• Remember that συν- assimilates to what follows: συν + μαθητής -> συμμαθητής, συν + κάτοικος -> συγκάτοικος, but συνεργάζομαι, συνάδελφος.
• Augmentatives are spoken register and usually mean “impressive” rather than literally “large”: μια ταινιάρα is a great film, μια καφεδάρα a serious coffee. Keep them out of formal writing.
• If you cannot recall the accepted compound, do not build one - use a phrasal compound or two separate words (λέξη-κλειδί, παιδί-θαύμα). Coining a plausible-sounding non-word is the one error that always shows.