Bit of a fidget, you understand (3)
I believe the answer is:
get
'understand' is the definition.
(getting is a kind of understanding)
'bit of a fidget you' is the wordplay.
'bit of' says the answer is hidden in the clue.
'GET' can be found hidden inside 'fidget you'.
(Other definitions for get that I've seen before include "Fetch or obtain" , "Acquire" , "See 18" , "Procure or secure" , "Receive; obtain" .)