Learn French: Je déballe les cartons et je trouve deux casse-noix. - I unpack the boxes and I find two nutcrackers.

Casse-noix is a compound noun made of a verb (casse) and a noun (noix). In verb-noun compounds, the verb part never takes a plural marker. The noun part usually takes an -s or -x in the plural, but since noix already ends in an -x in its singular form, it remains unchanged. Therefore, it is spelled the same way in both singular and plural.

Is casse in casse-noix a conjugated verb?

Yes, it is the third-person singular present tense form of casser (to break or crack). Most verb-noun compound nouns in French are built this way, using the il/elle form of the verb followed by a direct object, such as un gratte-ciel (a skyscraper) or un porte-manteau (a coat rack).

Even though noix is feminine, is casse-noix masculine?

Yes, it is masculine (un casse-noix, des casse-noix). As a highly reliable rule, almost all compound nouns formed with a verb and a noun are masculine in French, completely regardless of the gender of the noun used inside them.

I thought carton meant cardboard. Why does it translate to boxes here?