fangyoudaoicibaDictYouDict[fang 词源字典]
fang: [11] Fang originally meant ‘prey, spoils’ – a sense which survived well into the 18th century (‘Snap went the sheers, then in a wink, The fang was stow’d behind a bink [bench]’, Morrison, Poems 1790). It was related to a verb fang ‘take, capture’ which was very common in the Old and Middle English period, and which, like its surviving cousins German fangen, Dutch vangen, and Swedish fånga, goes back to a prehistoric Germanic *fangg- (English newfangled [15] is a memory of it).

The application of the word to an animal’s tooth does not emerge until as late as the 16th century, and although the broad semantic connection between ‘seizing’ and ‘sharp canine tooth’ is clear, the precise mechanism behind the development is not known.
=> newfangled[fang etymology, fang origin, 英语词源]
fang (n.)youdaoicibaDictYouDict
Old English fang "prey, spoils, plunder, booty; a seizing or taking," from gefangen, strong past participle of fon "seize, take, capture," from Proto-Germanic *fango- (cognates: Old Frisian fangia, Middle Dutch and Dutch vangen, Old Norse fanga, German fangen, Gothic fahan), from PIE root *pag- "to make firm, fix;" connected to Latin pax (genitive pacis) "peace" (see pact).

The sense of "canine tooth" (1550s) was not in Middle English and probably developed from Old English fengtoð, literally "catching- or grasping-tooth." Compare German Fangzahn. Transferred to the venom tooth of a serpent, etc., by 1800.