I diet, pass out and fade away (9)
I believe the answer is:
dissipate
'fade away' is the definition.
(thesaurus)
'i diet pass out' is the wordplay.
'out' is an anagram indicator (out can mean wrong or inaccurate).
'i'+'diet'+'pass'='idietpass'
'idietpass' is an anagram of 'DISSIPATE'.
'and' is the link.
(Other definitions for dissipate that I've seen before include "scatter" , "Exhaust" , "Waste (money/energy)" , "drive away" , "Fritter away" .)