flim-flam (n.)

also flimflam, 1530s, a contemptuous echoic construction, perhaps connected to some unrecorded dialectal word from Scandinavian (compare Old Norse flim "a lampoon"). From 1650s as a verb. Related: Flim-flammer.

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Definitions of flim-flam from WordNet

flim-flam (v.)
deceive somebody;
Synonyms: play a joke on / play tricks / trick / fob / fox / pull a fast one on / play a trick on