The Collaborative International Dictionary of English v.0.48:

Custodian \Cus*to"di*an\ (k?s-t?"d?-an), n. [From Custody.]
   One who has care or custody, as of some public building; a
   keeper or superintendent.
   [1913 Webster]

WordNet (r) 3.0 (2006):

custodian
    n 1: one having charge of buildings or grounds or animals [syn:
         custodian, keeper, steward]

Moby Thesaurus II by Grady Ward, 1.0:

61 Moby Thesaurus words for "custodian":
   MC, air warden, attendant, attorney, bailiff, bull, butler,
   caretaker, castellan, cerberus, char, charwoman, cleaner,
   cleaner-off, cleaner-up, cleaning lady, cleaning man,
   cleaning woman, commandant, conservator, croupier, curator, custos,
   emcee, factor, forest ranger, game warden, gamekeeper, gaoler,
   governor, guard, guardian, guardian angel, housekeeper, jailer,
   janitor, janitress, keeper, landreeve, librarian, lifeguard,
   lifesaver, majordomo, master of ceremonies, next friend, overseer,
   principal keeper, prison guard, prochein ami, proctor, procurator,
   ranger, screw, seneschal, shepherd, steward, supervisor, turnkey,
   warden, warder, watchdog