a cone-shaped surgical instrument designed to avoid penetration of the brain when incising the skull
Word origin
[1690–1700; ‹ Gk (trýpanon) abáptiston (trepan) not dipped, neut. of abáptistos, equiv. to a-a-6 + baptis-, var. s. of baptízein to immerse ( see baptize) + -tos verbal adj. suffix]