\Fum\, v. i. To play upon a fiddle. [Obs.] Follow me, and fum as you go. --B. Jonson.
[XEROX PARC] At PARC, often the third of the standard metasyntactic variables (after foo and bar). Competes with baz, which is more common outside PARC.
[jargon file]
Webster's 1913 Dictionary