drill bit vs rock bit

drill bit and rock bit both are nouns.

Word	Noun	Adjective	Verb	Adverb
drill bit	Yes	No	No	No
rock bit	Yes	No	No	No

As nouns, rock bit is a hyponym of drill bit; that is, rock bit is a word with a more specific, narrower meaning than drill bit:

Other hyponyms of drill bit include core bit, blade bit, fishtail bit, roller bit.

drill bit (noun)	rock bit (noun)
a bit used in drilling for oil	a drill bit that has hardened rotating rollers