WordReference Random House Unabridged Dictionary of American English © 2020
coun•ter•bore (koun′tər bôr′, -bōr′; koun′tər bôr′, -bōr′),USA pronunciation n., v., -bored, -bor•ing.
- Buildinga tool for enlarging a drilled hole for a portion of its length, as to permit sinking a screw head.
- Buildingthe portion of the hole so enlarged.
- Buildingto enlarge (a drilled hole) along part of the length of the hole by drilling with a bit having a greater diameter.
- counter- + bore1 1605–15