Ineffective (5-5)
'ineffective' is the definition.
(associated in meaning)
This is all the clue.
(Other definitions for useless that I've seen before include "Of no practical or worthwhile application" , "idle" , "Having no beneficial function" , "Worth zilch" , "Poor" .)
(Other definitions for wishy-washy that I've seen before include "Watered-down" , "Ineffectual" , "Diluted" , "Feeble, insipid" , "Bland -- pale" .)