tang n.

Old English tange, tang "tongs, pincers, foreceps, instrument for holding and lifting," from Proto-Germanic *tango (source also of Old Saxon tanga, Old Norse töng, Swedish tång, Old Frisian tange, Middle Dutch tanghe, Dutch tang, Old High German zanga, German Zange "tongs"), literally "that which bites," from PIE root *denk- "to bite" (source also of Sanskrit dasati "biter;" Greek daknein "to bite," dax "biting"). For sense evolution, compare French mordache "tongs," from mordre "to bite."

 Old English tunge "tongue, organ of speech; speech, a people's language," from Proto-Germanic *tungō (source also of Old Saxon and Old Norse tunga, Old Frisian tunge, Middle Dutch tonghe, Dutch tong, Old High German zunga, German Zunge, Gothic tuggo), from PIE root *dnghu- "tongue."

For substitution of -o- for -u-, see come. The spelling of the ending of the word apparently is a 14c. attempt to indicate proper pronunciation, but the result is "neither etymological nor phonetic, and is only in a very small degree historical" [OED]. In the "knowledge of a foreign language" sense in the Pentecostal miracle, from 1520s. Tongue-tied is first recorded 1520s. To hold (one's) tongue "refrain from speaking" was in Old English. Johnson has tonguepad "A great talker."

Bewar of tungis double and deceyuable,

Which with ther venym infect ech companye,

Ther poynaunt poisoun is so penetrable.

[John Lydgate, Fall of Princes (c. 1439)]

1875, from tang + -y (2). Figurative use by 1948. Related: Tanginess.