hand-waving

Short definition from Wiktionary

Noun

1. 1
   Alternative spelling of hand waving.
2. 2
   Discussion or argumentation involving approximation, vagueness, educated guessing, or the attempt to explain or excuse vagaries.

Adjective

1. 1
   Alternative spelling of handwaving.

Verb

1. 1
   present participle and gerund of hand-wave