Meh (4)
'meh' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for blah that I've seen before include "bunkum!" , "Pretentious nonsense" , "Rhubarb" , "Pretentious waffle" , "Bombast" .)
(Other definitions for soso that I've seen before include "mediocre" , "Indifferent" .)