Part of the theorem overcompensates for shift (6)
I believe the answer is:
remove
'shift' is the definition.
(removing is a kind of shifting)
'part of the theorem overcompensates for' is the wordplay.
'part of' indicates the answer is hidden within the clue.
'REMOVE' can be found hidden inside 'theorem overcompensates for'.
(Other definitions for remove that I've seen before include "Bunter's form" , "Takeaway" , "Get rid of, take away (6)" , "class in school" , "Take away or extract" .)