In short

Portuguese builds new words in two ways - by derivation (gluing a prefix or suffix onto a stem: fazer -> desfazer, informar -> informação) and by composition (welding two words together: guardar + chuva -> guarda-chuva). Spotting these patterns unlocks vocabulary you have never met. The flip side is that compound and irregular nouns do not pluralise like ordinary ones: guarda-chuva becomes guarda-chuvas but couve-flor becomes couves-flores, and a whole class of words such as ovo and porco change their vowel sound in the plural without changing a single letter. This lesson gives you the rules for all three.

The rule

Derivation: prefixes and suffixes

A prefix goes in front of a stem and mostly changes the meaning, not the word class: des- undoes or negates (fazer -> desfazer, gostar -> desgostar, ligar -> desligar), in-/im- means “not” (feliz -> infeliz, possível -> impossível, certo -> incerto), re- means “again” (fazer -> refazer, ler -> reler).

A suffix goes on the end and usually changes the word class: -ção/-são turns a verb into a noun (informar -> informação, decidir -> decisão), -dor makes an agent (trabalhar -> trabalhador, jogar -> jogador), -mente turns an adjective into an adverb (rápido -> rapidamente, from lesson 17), -eza/-ez makes an abstract quality noun (belo -> beleza, rígido -> rigidez). The affectionate -inho and the big -ão are suffixes too, but they get their own treatment in lesson 41.

Composition: compound words

A compound fuses two words into one idea. A few fuse completely (girassol, pontapé), but most keep a hyphen: guarda-chuva (umbrella), guarda-roupa (wardrobe), segunda-feira (Monday), couve-flor (cauliflower), porta-voz (spokesperson), fim de semana (weekend, no hyphen since the 1990 spelling agreement). The internal shape matters, because the plural depends on what each part is - a verb, a noun, an adjective, or a linking preposition.

The plural of compound nouns

Ask what the pieces are:

• Noun + noun, noun + adjective, or adjective + noun: both parts take the plural. segunda-feira -> segundas-feiras, couve-flor -> couves-flores, obra-prima -> obras-primas, amor-perfeito -> amores-perfeitos.
• Verb + noun: the verb is invariable, so only the noun changes. guarda-chuva -> guarda-chuvas (guarda here is the verb “guards”), porta-voz -> porta-vozes, beija-flor -> beija-flores, guarda-roupa -> guarda-roupas.
• Parts joined by a preposition: only the first noun changes. pé-de-meia -> pés-de-meia, fim de semana -> fins de semana, mão de obra -> mãos de obra.
• Watch guarda: in guarda-chuva it is the verb (invariable), but o guarda meaning “the guard” is a noun, so guarda-noturno -> guardas-noturnos pluralises both parts.

Metaphonic plurals: the invisible change

A group of masculine nouns has a closed ô sound in the singular that opens to ó in the plural. The spelling never changes - both are written with a plain o - so this plural is invisible on the page and audible only in speech: ovo -> ovos, porco -> porcos, osso -> ossos, fogo -> fogos, jogo -> jogos, olho -> olhos, povo -> povos, porto -> portos. Not every -o noun does it: bolo -> bolos and gosto -> gostos keep the closed vowel throughout. There is no rule to apply - you learn the “opening” ones as a list, the way a native ear already knows them.

Agreement of compound adjectives

When two adjectives form a compound, only the last one agrees; the first freezes in the masculine singular: luso-brasileiro -> relações luso-brasileiras, político-social -> questões político-sociais, técnico-científico -> áreas técnico-científicas. Two exceptions to keep: surdo-mudo makes both parts agree (surdos-mudos), and colour compounds are invariable - calças azul-marinho, camisolas verde-garrafa and laços cor-de-rosa never change.

Forms & patterns

Derivation at a glance:

Plural of compound nouns:

Metaphonic plural (spelling identical, vowel opens ô -> ó):

Examples

Common mistakes

• guardas-chuvas -> guarda-chuvas - the first part is the verb guardar, so it is invariable; only chuva takes the plural.
• couve-flores -> couves-flores - two nouns, so both are pluralised, not just the second one.
• fins de semanas -> fins de semana - when a preposition links the parts, only the first noun changes; semana stays singular.
• relações luso-brasileiros -> luso-brasileiras - in a compound adjective only the last element agrees; luso- is frozen, but -brasileiras must match relações.
• calças azuis-marinhos -> azul-marinho - colour compounds are invariable and take neither gender nor number.
• surdos-mudo -> surdos-mudos - surdo-mudo is the special case where both adjectives agree.
• guarda-noturnos -> guardas-noturnos - here guarda is the noun “guard”, not the verb, so both parts take the plural.

Tips

• Before pluralising a compound, name the parts: verb + noun means only the noun moves (guarda-chuvas); noun + noun means both move (couves-flores). That one question settles most cases.
• Prepositions freeze whatever follows them: pés-de-meia, mãos de obra, fins de semana - only the word before de ever changes.
• For compound adjectives, remember “last one only” (questões socioeconómicas agree just on the tail), and treat colours (azul-marinho, cor-de-rosa) as permanently invariable.
• The metaphonic plural is a listening and speaking skill, not a spelling one: since ovo and ovos look identical, drill the ear on the common set (ovo, porco, osso, fogo, jogo, olho, povo, porto) until the vowel opening is automatic.
• Use derivation to guess meaning: see des- and think “undo / opposite”, see -dor and think “the person or thing that does it”, see -mente and think “adverb”. It multiplies your vocabulary for free.
• In Brazil: the compound-plural and metaphony rules are the same; the vowel opening in the plural (ovos, jogos) happens in both norms - it is just easier to hear in European Portuguese, because the surrounding unstressed vowels are reduced so heavily.