Origin and history of whang

"strip cut from a piece of leather," Old English þwong, þwang "narrow strip of leather" (especially used from late Old English of a strap for a particular purpose, as a cord or whip or a band for fastening), from Proto-Germanic *thwang- (source also of Old Norse þvengr), said in Watkins to be from PIE root *twengh- "to press in on, to restrain" (source also of Old English twengan "to pinch, squeeze").

In reference to a kind of sandal, by 1965 (thong sandals); as a kind of bikini briefs, by 1990. In 15c., to cut large thongs of other men's leather was a figure for the comparative wastefulness likely accompany use of what is another's. As an adjective, thonged is attested from mid-15c. as "flogged."