"leave, sanction; the act of allowing," early 15c., permissioun, from Old French permission and directly from Latin permissionem (nominative permissio) "a giving up, a yielding; permission," noun of action from past-participle stem of permittere (see permit (v.)).
he asked permission to leave
permeant
permeate
permeation
Permian
permissible
permission
permissive
permit
permutate
permutation
permute