rock drill vs cross bit

rock drill and cross bit both are nouns.

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

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

Other hyponyms of rock drill include star drill, straight-fluted drill, straight flute.

rock drill (noun)	cross bit (noun)
a drill for penetrating rock	a rock drill having cruciform cutting edges; used in mining