Why does 'mohínes' have an accent?

Question

I came across the following sentence in El año del diluvio by Eduardo Mendoza:

La guardesa depositó la bandeja y se marchó haciendo mohínes

Why does mohínes have an accent? According to WordReference the singular is mohín. As far as I was aware, singular nouns that have a stress on the last syllable – like organización – lose the written accent in the plural – organizaciones. This is because in words without a written accent (and ending with a vowel, n, or s), the stress is assumed to fall on the penultimate syllable. If mohín followed this rule, then shouldn't the plural be mohines?

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Encontré la siguiente oración en El año del diluvio por Eduardo Mendoza:

La guardesa depositó la bandeja y se marchó haciendo mohínes

¿Porqué lleva mohínes un acento? Según WordReference, el singular es mohín. A mi entiendo, sustantivos singulares que llevan agudo en la sílaba última – como organización – pierden el agudo en el plural – organizaciones. Esto se debe al hecho de que el acento de las palabras sin agudo (y terminado con s), cae en la sílaba penúltima. Si mohín cumpliera esa regla, sería mohines en el plural.

Answer 1

In this case I think you are (understandably) being misled by the medial h. The h is not only mute, but also it doesn't have any effect on syllable division.¹ So you must imagine mohín would have the same written acute accent if it were written *moín. It's not the case that the h in mohín is making -hín a separate syllable; that is being marked by the acute accent.

In Spanish, "open" vowels a, e and o usually form diphthongs with "closed" vowels i and u. When they don't it's because the "closed" vowel is stressed, and this stress is always orthographically marked by the acute accent.

The o and the í are in hiatus, i.e. they don't form a diphthong as they normally would. The acute accent over í marks both stress and the fact that the í is on a different syllable: mo-hín, mo-hí-nes.

If you didn't write an acute accent in mohín and mohínes, they would be pronounced as moin and moines, i.e. as you would pronounce (in English) "moyn" and "moy-ness". Again, the h is totally irrelevant. The same thing, where the h doesn't break the diphthong, takes place in búho; and the same kind of thing that happens with mohín happens with maíz (pl. maíces) and tahúr (pl. tahúres).

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^{1. "La presencia de una hache intercalada no exime de la obligación de tildar la vocal tónica del hiato: búho, ahíto, prohíbe."
(DPD: Tilde - 2.2.2.b Acentuación de las palabras con hiato)}