— counterborer , n.
/kown"teuhr bawr', -bohr'; kown"teuhr bawr", -bohr"/ , n. , v. , counterbored, counterboring .
n.
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.
v.t.
3. to enlarge (a drilled hole) along part of the length of the hole by drilling with a bit having a greater diameter.
[ 1605-15; COUNTER- + BORE 1 ]