lac

Lac, lactis is third declension neuter, and the nominative is a stump: the stem is lact-, and the final t has simply fallen off the nominative and accusative, which are both lac. Genitive lactis, ablative lacte. There is no plural worth the name, as with most substances.

It pairs constantly with mel, "honey", in the biblical formula terra lacte et melle manans, and both are neuters of the same awkward type. The word is generous with descendants: lactis gives Italian latte, French lait and Spanish leche, and English took lactose, lactate, lactic and, at a distance, lettuce, which the Romans named lactuca for the milky sap it bleeds when cut.