Heard I was hard? Nonsense (7)
I believe the answer is:
eyewash
'nonsense' is the definition.
(thesaurus)
'heard i was hard?' is the wordplay.
'heard' indicates a 'sounds like' (homophone) clue.
'hard?' becomes 'h'.
'i' is a homophone of 'eye'.
'eye'+'was'+'h'='EYEWASH'
(Other definitions for eyewash that I've seen before include "Nonsense (informal)" , "Visual cleansing agent - nonsense" , "rot?" , "Balderdash" , "Insincere talk or optical lotion" .)