a crown-saw or cylindrical saw for perforating the skull, turned, when used, like a bit or gimlet. see trephine.-a kind of broad chisel for sinking shafts.-to perforate (the skull) with a trepan, so as to remove a portion of the bone, and thus relieve the brain from pressure or irritation; to perform an operation with the trepan.-a snare; a trapan.-a deceiver; a cheat.-to insnare; to trap; to trapan.