Source : Webster's Revised Unabridged Dictionary (1913)

Permissible \Per*mis"si*ble\, a.
   That may be permitted; allowable; admissible. --
   {Per*mis"si*ble*ness}, n. -- {Per*mis"si*bly}, adv.

Source : WordNet®

permissibly
     adv : in a permissible manner [syn: {allowably}] [ant: {impermissibly}]