lin·go (lngg) KEY
Probably from Portuguese lingoa, from Latin lingua, language; see dgh- in Indo-European roots
A look at the entry in the Indo-European roots entry for *dgh- will show that the words tongue, language, and lingo are related, all going back to the Indo-European root *dgh-, "tongue." The relationship between language and lingo is not particularly surprising given their related meanings and common root, but one might be curious about the routes by which these two words came into English. Language, as did so many of our important borrowings from Latin, passed through French into English during the Middle Ages, the forms involved being Latin lingua, "language," its descendant, Old French langue, and its derivative, langage. Lingo, on the other hand, entered English after the end of the Middle Ages when Europe had opened itself to the larger world. We have probably borrowed lingo from lingoa, a Portuguese descendant of Latin lingua. The Portuguese were great traders before the English were, and the sense "foreign language" was likely strengthened as the Portuguese traveled around the world. Interestingly enough, the first recorded instance of lingo in English is in the New World (1660) in a reference to the "Dutch lingo." The development in sense to "unintelligible language" and "specialized language" is an obvious one.