countersink bit vs counterbore

countersink bit and counterbore both are nouns.

Word	Noun	Adjective	Verb	Adverb
countersink bit	Yes	No	No	No
counterbore	Yes	No	No	No

As nouns, countersink bit and counterbore are synonyms defined as:

countersink bit and counterbore: a bit for enlarging the upper part of a hole

Other synonyms of countersink bit include countersink.

countersink bit (noun)	counterbore (noun)
a bit for enlarging the upper part of a hole	a bit for enlarging the upper part of a hole