Tren"ton pe"ri*od (?). (Geol.) A subdivision in the lower Silurian
system of America; — so named from Trenton Falls, in New York. The
rocks are mostly limestones, and the period is divided into the
Trenton, Utica, and Cincinnati epochs. See the Chart of Geology.
Tre*pan" (?), n. [F. trépan (cf. Sp. trépano, It. trepano, trapano),
LL. trepanum, fr. Gr. &?; a borer, auger, trepan, fr. &?; to bore, &?;
a hole. Cf. Trephine.] 1. (Surg.) A crown-saw or cylindrical saw for
perforating the skull, turned, when used, like a bit or gimlet. See
Trephine.