1. 
[syn: permissible, allowable]
2.  that may be accepted or conceded; 
- Example: "a kind of speculation that was permissible in cosmology but inadmissible in medicine"
The Collaborative International Dictionary of English v.0.48:
Permissible \Per*mis"si*ble\, a.
   That may be permitted; allowable; admissible. --
   Per*mis"si*ble*ness, n. -- Per*mis"si*bly, adv.
   [1913 Webster]
WordNet (r) 3.0 (2006):
permissible
    adj 1: that may be permitted especially as according to rule;
           "permissible behavior in school"; "a permissible tax
           deduction" [syn: permissible, allowable] [ant:
           impermissible]
    2: that may be accepted or conceded; "a kind of speculation that
       was permissible in cosmology but inadmissible in medicine"
Moby Thesaurus II by Grady Ward, 1.0:
31 Moby Thesaurus words for "permissible":
   OK, acceptable, admissible, all right, allowable, allowed,
   approved, authorized, bearable, endorsed, excusable, justifiable,
   kosher, lawful, legal, legit, legitimate, legitimized, licit, okay,
   pardonable, permitted, proper, sanctionable, sanctioned, tolerable,
   tolerated, unforbidden, unprohibited, venial, warrantable