"I've seen better" (3)
I believe the answer is:
meh
'i've seen better' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for meh that I've seen before include "Who cares" , "expression of indifference" , "Unexciting (modern slang)" , "Not much cop" , "am I bovvered?" .)