Why does -ão have three different plurals?

Historically the ending -ão merged several Latin endings, so it pluralises three ways. The large majority become -ões (leão/leões, ação/ações). A small closed set becomes -ãos (mão/mãos, irmão/irmãos, cidadão/cidadãos), and another small set becomes -ães (pão/pães, cão/cães, alemão/alemães). The tool keeps explicit lists for the two small sets and defaults the rest to -ões.

How are words ending in -l handled?

The final l is dropped and -is is added, with an accent where the stress needs it: -al becomes -ais (animal/animais), -el becomes -éis (papel/papéis), -ol becomes -óis (lençol/lençóis), and -ul becomes -uis. Words in -il split by stress: oxytones add -is (funil/funis) while paroxytones become -eis (fóssil/fósseis).

Which words ending in -s stay the same?

Paroxytone words (stress on the second-to-last syllable) ending in -s are invariable: lápis, ônibus, and vírus do not change. Oxytones and monosyllables ending in -s add -es and drop a final accent, so mês becomes meses, gás becomes gases, and país becomes países.

What about -m and -r/-z endings?

Words ending in -m change the m to -ns (homem/homens, jardim/jardins, som/sons). Words ending in -r, -z, or -n add -es (flor/flores, luz/luzes, hífen/hifens).

Does it know proper nouns or invariable words?

It applies regular and well-known irregular rules but does not have a full dictionary, so it cannot detect that a specific word is invariable for lexical reasons. It correctly handles the structural invariables (paroxytone -s and -x endings) and the closed -ão sets, and reports the rule it used so you can verify.

Portuguese Plural Helper

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This tool forms the plural of a Portuguese noun or adjective and tells you which rule it applied. Portuguese plurals are mostly regular, but the ending -ão and the -l endings have real complications that a simple add-an-s approach gets wrong.

How it works

The word is matched against the plural rules in order, and the first matching rule fires:

leão     -> leões      (common -ão class)
mão      -> mãos       (closed -ãos set)
pão      -> pães       (closed -ães set)
animal   -> animais    (-al -> -ais)
papel    -> papéis     (-el -> -éis)
fóssil   -> fósseis    (paroxytone -il -> -eis)
homem    -> homens     (-m -> -ns)
lápis    -> lápis      (paroxytone -s, invariable)

The two small -ão sets (-ãos and -ães) are stored as explicit lists, since they cannot be predicted from spelling alone; every other -ão word defaults to the majority -ões. The -s and -il rules branch on stress, which the tool infers from accent marks and a curated list.

Tips and notes

Add the article (o, a, um, uma) and the tool pluralises it too: o leão becomes os leões. Because no automatic system can know every lexical exception, treat the named rule as the explanation and double-check rare or specialised vocabulary. The default word leão shows the most common -ão class; try pão and mão to see the two irregular classes side by side.