Either didn’t remove or took off (4)
I believe the answer is:
left
'took off' is the definition.
The answer and definition can be both related to change as well as being past participle verbs.
Perhaps you can see a link between them that I can't see?
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for left that I've seen before include "Departed, went away" , "not consumed" , "walk-out?" , "choice at a junction?" , "Punch, perhaps" .)