Meaning

noun 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

noun a bit for enlarging the upper part of a hole

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

originEtymology tree Proto-Indo-European *ḱe? Proto-Indo-European *ḱóm Proto-Italic *kom Proto-Italic *kom- Proto-Indo-European *-teros Proto-Italic *-teros Proto-Italic *komterosder. Proto-Italic *komterād Latin contrāder. Old French contre- Anglo-Norman countre-bor. Middle English counter- English counter- English sink English countersink From counter- + sink.

Etymology from Wiktionary, CC BY-SA 3.0