permissible (adj.)

early 15c., permitten, transitive, "allow (something) to be done, suffer or allow to be," from Old French permetre and directly from Latin permittere "let pass, let go, let loose; give up, hand over; let, allow, grant, permit," from per "through" (from PIE root *per- (1) "forward," hence "through") + mittere "let go, send" (see mission). Meaning "grant liberty or leave" is from 16c. Related: Permitted; permitting.

1814, from assimilated form of in- "not, opposite of" (see in- (1)) + permissible.