char vs bone black

char and bone black both are nouns.

Word	Noun	Adjective	Verb	Adverb
char	Yes	No	Yes	No
bone black	Yes	No	No	No

As nouns, bone black is a hyponym of char; that is, bone black is a word with a more specific, narrower meaning than char:

char: a charred substance
bone black: black substance containing char in the form of carbonized bone; used as a black pigment

Other hyponyms of char include animal black, animal charcoal, bone char, snuff.

char (noun)	bone black (noun)
any of several small trout-like fish of the genus Salvelinus	black substance containing char in the form of carbonized bone; used as a black pigment
a human female employed to do housework
a charred substance

char (verb)	bone black (verb)
burn slightly and superficially so as to affect color
burn to charcoal