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onyx [onyx 词源字典]: onyx: [13] Greek ónux meant ‘claw, fingernail’ (it is distantly related to English nail). Certain sorts of onyx are pink with white streaks, and a resemblance to pink fingernails with their paler crescent-shaped mark at the base led the Greeks to name the stone ónux. The word travelled to English via Latin onyx and Old French onix.
=> nail[onyx etymology, onyx origin, 英语词源]
finger-nail (n.): also fingernail, early 13c., from finger (n.) + nail (n.).
manicure (n.): 1873, "one who professionally treats hands and fingernails," from French manicure, literally "the care of the hands," from Latin manus "hand" (see manual) + cura "care" (see cure (n.1)). Meaning "treatment and care of the hands and fingernails" is attested from 1887.
nail (n.): Old English negel "metal pin," nægl "fingernail (handnægl), toenail," from Proto-Germanic *naglaz (cognates: Old Norse nagl "fingernail," nagli "metal nail;" Old Saxon and Old High German nagel, Old Frisian neil, Middle Dutch naghel, Dutch nagel, German Nagel "fingernail, small metal spike"), from PIE root *(o)nogh "nail" (cognates: Greek onyx "claw, fingernail;" Latin unguis "nail, claw;" Old Church Slavonic noga "foot," noguti "nail, claw;" Lithuanian naga "hoof," nagutis "fingernail;" Old Irish ingen, Old Welsh eguin "nail, claw").

The "fingernail" sense seems to be the original one. Nail polish attested from 1891. To bite one's nails as a sign of anxiety is attested from 1570s. Nail-biting is from 1805. Hard as nails is from 1828. To hit the nail on the head "say or do just the right thing" is first recorded 1520s. Phrase on the nail "on the spot, exactly" is from 1590s, of obscure origin; OED says it is not even certain it belongs to this sense of nail.
onyx (n.): mid-13c., from Old French oniche "onyx" (12c.), and directly from Latin onyx (genitive onychis), from Greek onyx "onyx-stone," originally "claw, fingernail" (see nail (n.)). So called because the mineral's color sometimes resembles that of a fingernail, pink with white streaks.
paronychia (n.): inflammation beside a fingernail, 1590s, from Latin, from Greek paronykhia "whitlow," from para- "beside" (see para- (1)) + onyx "nail" (see nail (n.)) + abstract noun ending -ia.