Irregular plurals: gosti, sati; očiju, ruku

Monosyllables that refuse the infix

You learned that short masculine nouns stretch their plural with -ovi/-evi (grad → gradovi, sin → sinovi). A closed set of everyday monosyllables refuses the infix and takes bare -i:

You have used these all along — Gosti dolaze u sedam sati. — this lesson just names the rule: memorize the members, because *gostovi is wrong.

Genitive plurals worth their own row

A few body-part and people nouns take genitive plural -iju: oko → oči → očiju, uho → uši → ušiju, gost → gostiju, prst → prstiju. Ne vjerujem svojim ušima: sto gostiju!

ruka and noga keep an old dual genitive: pet ruku, pet nogu — never *ruka or *noga after numbers. Stol ima četiri noge, a pas nema ruku.