bite (v.)youdaoicibaDictYouDict
Old English bitan (class I strong verb; past tense bat, past participle biten), from Proto-Germanic *bitan (cognates: Old Saxon bitan, Old Norse and Old Frisian bita, Middle Dutch biten, Dutch bijten, German beissen, Gothic beitan "to bite"), from PIE root *bheid- "to split, crack" (see fissure).

To bite the bullet is said to be 1700s military slang, from old medical custom of having the patient bite a lead bullet during an operation to divert attention from pain and reduce screaming. Figurative use from 1891; the custom itself attested from 1840s. To bite (one's) tongue "refrain from speaking" is 1590s. To bite the dust "die" is 1750 (Latin had the same image; compare Virgil's procubuit moriens et humum semel ore momordit). To bite off more than one can chew (c. 1880) is U.S. slang, from plug tobacco.
gnaw (v.)youdaoicibaDictYouDict
Old English gnagan "to gnaw, bite off little by little" (past tense *gnog, past participle gnagan), from Proto-Germanic *gh(e)n- "to gnaw" (cognates: Old Saxon gnagan, Old Norse, Swedish gnaga, Middle Dutch, Dutch knagen, Old High German gnagan, German nagen "to gnaw"), probably imitative of gnawing. Figurative sense "wear away as if by continued biting" is from early 13c. Related: Gnawed; gnawing.