bone vs grind away

bone is a noun but grind away is not a noun.

Word	Noun	Adjective	Verb	Adverb
bone	Yes	Yes	Yes	No
grind away	No	No	Yes	No

As verbs, bone and grind away are synonyms defined as:

Other synonyms of bone include bone up, cram, drum, get up, mug up, swot, swot up.

bone (noun)	grind away (noun)
a shade of white the color of bleached bones
rigid connective tissue that makes up the skeleton of vertebrates
the porous calcified substance from which bones are made

bone (adjective)	grind away (adjective)
consisting of or made up of bone

bone (verb)	grind away (verb)
remove the bones from	study intensively, as before an exam
study intensively, as before an exam