DRILL (Sax. thirlian, to perforate; Ger. drillen, to turn, to twist), a tool with a steel point, used for perforating metal, ivory, and other hard substances. It is worked by a moderate pressure, with a whirling motion, which is usually communicated to it either by a drill-bow, or by means of a nut made to play on a spiral shaft in the end of which the steel point is fixed. The extremity of the borer is generally somewhat flattened, and of an angular shape, thus \sim, with sharp edges.