Are there any nouns with irregular plurals in Spanish?

Question

In English, some nouns have regular plural forms ending in -s or -es and fewer are irregular. Fish in the plural is still fish while child becomes children.

In Spanish, nearly all nouns are regular, adding -s or -es. The rule is even simpler than in English (-es is for words that end in consonants and accented vowels other than é, s for all others). Also, words that end in z change the z to c in the plural to retain a pleasing sound in all regional accents.

There are some words borrowed from other languages that have irregular plurals. In Mexico, the weekly markets are called tianguis (singular: tianguis plural: tianguis) after the Nahuatl word for the same weekly markets (often in the exact same places). Tianguis has been a common Spanish word since around A.D. 1520 but it still seems like a piece of traditional pre-hispanic Mexico.

Are there any native or fully absorbed Spanish nouns with irregular plurals?

Answer 1

You can find here the complete reference guide for plurals in Spanish by RAE. In that document you can read that there are some differences from the general rules, which aren't as simple as you described but are quite closed.

For example some words coming from other languages can have the same word for singular as for plural:

(from Latin) El currículum vitae  --> Los currículum vitae
(from French) El crómlech --> Los crómlech

Also, the stressed syllable doesn't change in plurals, but there are 3 exceptions that have different stressed syllable in singular than in plural:

1. Régimen (Ré-gi-men) -->Regímenes (Re-gí-me-nes)
2. Espécimen (Es-pé-ci-men) -->Especímenes(Es-pe-cí-me-nes)
3. Carácter (Ca-rác-ter) -->Caracteres(Ca-rac-te-res)

Answer 2

There is one entire class of nouns in Spanish which are all regular plurals of the type similar to English "sheep" and "fish" except instead of the singular also being the plural, the plural is also the singular.

There is a class of Spanish compound nouns formed by joining a verb with a plural noun. They are all masculine and always the same form is used for both singular and plural despite all ending in -s or -es.

In fact they are such a particular favourite of mine that I have been collecting them for years and I created a special place in Wiktionary to gather them into a category.

It ranges from really common ones like cumpleaños to ones I've never heard before like tumbaburros.

(There are probably other regular plurals, too, but I can't think of any just yet.)