handwave
[poss. from gestures characteristic of stage magicians] 1. v.
To gloss over a complex point; to distract a listener; to support
a (possibly actually valid) point with blatantly faulty logic. 2.
n. The act of handwaving. "Boy, what a handwave!"
If someone starts a sentence with "Clearly..."
or "Obviously..." or "It is self-evident
that...", it is a good bet he is about to handwave
(alternatively, use of these constructions in a sarcastic tone
before a paraphrase of someone else's argument suggests that it
is a handwave). The theory behind this term is that if you wave
your hands at the right moment, the listener may be sufficiently
distracted to not notice that what you have said is bogus. Failing that, if a listener does object,
you might try to dismiss the objection with a wave of your
hand.
The use of this word is often accompanied by gestures: both
hands up, palms forward, swinging the hands in a vertical plane
pivoting at the elbows and/or shoulders (depending on the
magnitude of the handwave); alternatively, holding the forearms
in one position while rotating the hands at the wrist to make
them flutter. In context, the gestures alone can suffice as a
remark; if a speaker makes an outrageously unsupported
assumption, you might simply wave your hands in this way, as an
accusation, far more eloquent than words could express, that his
logic is faulty.