borer vs star drill

borer and star drill both are nouns.

Word	Noun	Adjective	Verb	Adverb
borer	Yes	No	No	No
star drill	Yes	No	No	No

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

borer: a drill for penetrating rock
star drill: a steel rock drill with a star-shaped point that is used for making holes in stones or masonry; it is operated by hitting the end with a hammer while rotating it between blows

Other hyponyms of borer include cross bit, straight-fluted drill, straight flute.

borer (noun)	star drill (noun)
any of various insects or larvae or mollusks that bore into wood	a steel rock drill with a star-shaped point that is used for making holes in stones or masonry; it is operated by hitting the end with a hammer while rotating it between blows
a drill for penetrating rock