"allowable, proper to be allowed," early 15c., from Old French permissible (15c.) and directly from Medieval Latin permissibilis, from permiss-, past-participle stem of Latin permittere "let pass, let go; grant, permit" (see permit (v.)).
permissible behavior in school
a permissible tax deduction
a kind of speculation that was permissible in cosmology but inadmissible in medicine