The Collaborative International Dictionary
Knife switch \Knife switch\ (Elec.) A switch consisting of one or more knifelike pieces hinged at one end and making contact near the other with flat gripping springs.
Wiktionary
n. A switch used to control the flow of electricity in a circuit, consisting of a hinge which allows a metal lever, or knife, to be lifted from or inserted into a slot or jaw.
Wikipedia
A knife switch is a type of switch used to control the flow of electricity in a circuit. It is composed of a hinge which allows a metal lever, or knife, to be lifted from or inserted into a slot or jaw. The hinge and jaw are both fixed to an insulated base, and the knife has an insulated handle to grip at one end. Current flows through the switch when the knife is pushed into the jaw. Knife switches can take several forms, including single throw, in which the "knife" engages with only a single slot, and double throw, in which the knife hinge is placed between two slots and can engage with either one. Also, multiple knives may be attached to a single handle and can be used to activate more than one circuit simultaneously.
Usage examples of "knife switch".
I cautioned the pressmen to stand back under the shelter, and gave the professor the knife switch that would send the rocket on its way.
Then he looped a length of fishline around the crosspiece of the knife switch and pushed both ends back through the upper hole in the panel from the back.
Mounted on it was a single three-position knife switch-that is, one with two slots for the blade, the third position being disengaged from either.
Keeping the variable-sword unostentatiously in sight, he closed the cover on the kzin's crash couch and flipped a knife switch.