The Collaborative International Dictionary of English v.0.48:

Monastic \Mo*nas"tic\, Monastical \Mo*nas"tic*al\, a. [Gr. ?
   monk: cf. F. monastique. See Monastery.]
   1. Of or pertaining to monasteries, or to their occupants,
      rules, etc., as, monastic institutions or rules.
      [1913 Webster]

   2. Secluded from temporal concerns and devoted to religion;
      recluse. "A life monastic." --Denham.
      [1913 Webster]

WordNet (r) 3.0 (2006):

monastical
    adj 1: of communal life sequestered from the world under
           religious vows [syn: cloistered, cloistral,
           conventual, monastic, monastical]