Dismiss as unimportant (8)
I believe the answer is:
belittle
'dismiss as unimportant' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for belittle that I've seen before include "Make to seem unimportant" , "Denigrate, diminish" , "Imply that person is inferior" , "Imply that person is of small value or unworthy" , "Disparage - minimise" .)