handwave verb to oversimplify or give a cursory explanation of a complicated point US
— Guy L. Steele, CoevolutionQuarterly, p. 31, Spring 1981: “Computer Slang”
If someone starts a sentence with “Clearly...” or “Obviously...” or “It is self-evident that...,” you can be sure he is about to handwave. — Guy L. Steele et al., TheHacker’sDictionary, p. 81, 1983