Give a little jerk when you switch on (5)

I believe the answer is:

start

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'switch on' is the definition.
(thesaurus)

I can't explain the rest of the clue.

(Other definitions for start that I've seen before include "Take the first step" , "Jerk" , "Begin - jump" , "Move quickly < when surprised" , "begin an argument?" .)

I've seen this clue in the Evening Standard.

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