One cuts decoration off (5)
I believe the answer is:
going
'off' is the definition.
(both can mean departing)
'one cuts decoration' is the wordplay.
I cannot quite see how this works, but
'one' could be 'o' (I've seen this in other clues) and 'o' is found in the answer.
The remaining letters 'ging' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
(Other definitions for going that I've seen before include "in action" , "on the way out" , "Moving away, departing" , "Available" , "fading" .)