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c.1600, "allowing to pass through," from Old French permissif, from Latin permiss-, past participle stem of permittere "to let go, let pass, let loose" (see permit (v.)). In sense of "tolerant, liberal" it is first recorded 1956; by 1966 it had definite overtones of sexual freedom. Earlier it meant "permitted, allowed" (early 15c.). Related: Permissively; permissiveness.