Pronunciation: (koun'tur-bôr", -bōr"; koun'tur-bôr', -bōr'), [key]
—n., v., -bored, -bor•ing.
1. a tool for enlarging a drilled hole for a portion of its length, as to permit sinking a screw head.
2. the portion of the hole so enlarged.
to enlarge (a drilled hole) along part of the length of the hole by drilling with a bit having a greater diameter.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.