Devaluate (7)
I believe the answer is:
detract
'devaluate' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for detract that I've seen before include "Belittle" , "Take away, character perhaps" , "Take away (from value of something)" , "Slight" , "Take away a part of, lower in value" .)