SWITCHBLADE
switchblade, switchblade knife, flick-knife, flick knife
(noun) a pocketknife with a blade that springs open at the press of a button
Source: WordNet® 3.1
Etymology
Noun
switchblade (plural switchblades)
A folding knife with a blade which opens automatically (under spring pressure) when a button is pressed.
Verb
switchblade (third-person singular simple present switchblades, present participle switchblading, simple past and past participle switchbladed)
(transitive) To attack or cut with a switchblade.
(intransitive) To spring open or up.
(ambitransitive) To (cause to) make a sudden move or transition.
Source: Wiktionary