1. [n]  a surgical instrument used to remove sections of bone from the skull
2. [v]  operate on with a trephine

TREPHINE is a 8 letter word that starts with T.

1. \Tre*phine"\ (?; 277), n. [A dim. of 1st trepan: cf. F.
   tr['e]phine.] (Surg.)
   An instrument for trepanning, being an improvement on the
   trepan. It is a circular or cylindrical saw, with a handle
   like that of a gimlet, and a little sharp perforator called
   the center pin.
   
   

2. \Tre*phine"\, v. t. [imp. & p. p. {Trephined}; p. pr. &
   vb. n. {Trephining}.]
   To perforate with a trephine; to trepan.