A bit of a fidget, you understand (3)
I believe the answer is:
get
'understand' is the definition.
(getting is a kind of understanding)
'a bit of a fidget you' is the wordplay.
'a bit of' indicates the answer is hidden within the clue (I've seen 'a bit' mean this (the answer is formed by a bit of the clue)).
'GET' can be found hidden inside 'fidget you'.
(Other definitions for get that I've seen before include "Acquire" , "Receive; obtain" , "Fetch or obtain" , "Understand" , "Procure from vegetables" .)