Mineralogy . a variety of chalcedony having straight parallel bands of alternating colors. Compare Mexican onyx .

(not used technically) an unbanded chalcedony dyed for ornamental purposes.

black, esp. a pure or jet black.

Medicine/Medical . a nail of a finger or toe.

black, esp. jet black.

adjective

ebon , ebony , inky , jet , jetty , pitch-black , pitchy , sable , sooty