grammar.nouns.compound-nouns
Compound nouns: el abrelatas, el sacacorchos
Verb + plural noun makes a masculine, invariable compound: el abrelatas, el paraguas, el lavaplatos. Noun + noun compounds pluralize the first word: hombres rana.
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Explicación
The most productive way Spanish builds compound nouns is verb + plural noun, fused into one word: abrir + latas → el abrelatas ('can opener'). Others: el sacacorchos, el paraguas, el lavaplatos, el parabrisas, el rascacielos, el cumpleaños. They are masculine and identical in singular and plural: el paraguas / los paraguas.
Because they already end in -s, the article is what marks number: el lavaplatos ('the dishwasher') vs los lavaplatos ('the dishwashers').
A different type is noun + noun (or noun + adjective), where the two words stay separate and the plural goes on the head (first) noun: el hombre rana → los hombres rana, la palabra clave → las palabras clave, una hora pico → horas pico.
Ejemplos
The dishwasher isn't working.
Región: global
We defined the project's keywords.
Región: global
The can opener and the corkscrew are in the drawer.