/on"iks, oh"niks/ , n.
1. Mineral. a variety of chalcedony having straight parallel bands of alternating colors. Cf. Mexican onyx .
2. (not used technically) an unbanded chalcedony dyed for ornamental purposes.
3. black, esp. a pure or jet black.
4. Med. a nail of a finger or toe.
adj.
5. black, esp. jet black.
[ 1250-1300; ME onix onyx ónyx nail, claw, veined gem ]