mid-14c., "to be foolish, act the fool," from fool (n.1). The transitive meaning "make a fool of" is recorded from 1590s. Sense of "beguile, cheat" is from 1640s. Also as a verb 16c.-17c. was foolify. Related: Fooled; fooling. Fool around is 1875 in the sense of "pass time idly," 1970s in sense of "have sexual adventures."
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Definitions of fooling from WordNet
characterized by a feeling of irresponsibility; "a broken back is nothing to be casual about; it is no fooling matter";