lingua

Lingua, linguae, f., first declension, and it runs the same three steps English does with "tongue": the organ in the mouth, then speech in general, then a particular language, lingua Latina. Because the metaphor is shared, the idioms transfer intact - linguam tenere really is "to hold one's tongue".

The older form of the word was dingua, and the l is thought to have crept in by contamination from lingo, "I lick". That d is why lingua looks so unlike English "tongue" despite the two descending from the same root. Spanish lengua and French langue continue it directly, and English took language, linguist, bilingual and the whole of lingua franca.