Source : Webster's Revised Unabridged Dictionary (1913)

Castellan \Cas"tel*lan\, n. [OF. castelain, F. ch[^a]telain, L.
   castellanus pertaining to a castle, an occupant of a caste,
   LL., a governor of a castle, fr. L. castellum castle,
   citadel, dim. of castrum fortified place. See {Castle}, and
   cf. {Chatelaine}.]
   A governor or warden of a castle.