tro·car 
(trōkär′)
(trōkär′)n.
A sharp-pointed surgical instrument, used with a cannula to puncture a body cavity for fluid aspiration.
[French trocart : trois, three (from Old French, from Latin trēs; see trei- in the Appendix of Indo-European roots) + carre, side of an instrument (from Old French, from carrer, to square, from Latin quadrāre, from quadrum, square; see kwetwer- in the Appendix of Indo-European roots).]