When talking about nouns, we remember that they are conceptualized as everything that gives names to entities in general: places, people, animals, things, among others.
And a doubt that naturally occurs, it is time to use the correct form of compound nouns, that is, those that have more than one radical in their composition. Like for example, umbrella, tomboy's foot, hummingbird, among others.
Taking into account that written language requires certain standards of employability, and that when referring to these we refer to the question of the rules, therefore, some specific cases follow, which we must refer to pay attention to:
# In compounds where the first element is a verb or an invariant word, such as an adverb, and the second element is a noun or adjective:
- Only the second element pluralizes. Note:
undersigned undersigned
hummingbird - hummingbirds
evergreen - evergreens
# In compounds where elements are variable:
- Both go to the plural. Ex:
deaf mute - deaf mute
civil guard - civil guards
wednesday - wednesdays
# In cases where the second element gives an idea of purpose or similarity, or limits the first:
- Only the first goes to the plural. Ex:
standard school – standard schools
carrier pigeon - carrier pigeon
family allowance - family allowance
# Verb+verb compounds:
- Both vary or only the second goes to the plural. Ex:
run-run - run-run or run-run
# Compounds linked by preposition:
- In this case, only the first goes to the plural. Ex:
tomboy's feet - tomboy's feet
sponge cake - sponge cake
# In compounds formed by repeated words or onomatopoeia:
- Only the second element goes to the plural. Ex:
optics - optics
reco-reco - reco-reco
ticking - ticking
By Vânia Duarte
Graduated in Letters
Brazil School Team
Grammar - Brazil School
Source: Brazil School - https://brasilescola.uol.com.br/gramatica/o-plural-dos-substantivos-compostos.htm