Trepan \Tre*pan"\, v. t. & i. [imp. & p. p. {Trepanned}; p. pr.
& vb. n. {Trepanning}.] [Cf. F. tr['e]paner. See {Trepan} a
saw.] (Surg.)
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.
[1913 Webster]