1822 C. Lamb in Mar. 282/1 In the latter [sc. puns], I include all non-serious subjects.
1939 17 368/2 Drunkenness, begging, vagrancy, similar misdemeanors were listed as non-serious.
1992 101 10 One should treat not-p as a non-serious possibility in a certain decision context..only if one adds p to the corpus of propositions.