counterbore vs countersink

counterbore and countersink both are nouns.

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

As nouns, counterbore and countersink are synonyms defined as:

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

Other synonyms of counterbore include countersink bit.

counterbore (noun)	countersink (noun)
a bit for enlarging the upper part of a hole	a bit for enlarging the upper part of a hole
	a hole (usually in wood) with the top part enlarged so that a screw or bolt will fit into it and lie below the surface

counterbore (verb)	countersink (verb)
	insert (a nail or screw below the surface, as into a countersink)