Attempt to include a singlet in disguise (8)
I believe the answer is:
travesty
'disguise' is the definition.
(thesaurus)
'attempt to include a singlet' is the wordplay.
'attempt' becomes 'try' (I've seen this before).
'to include' is an insertion indicator.
'singlet' becomes 'vest' ('vest' can be a synonym of 'singlet').
'a'+'vest'='avest'
'try' enclosing 'avest' is 'TRAVESTY'.
'in' acts as a link.
(Other definitions for travesty that I've seen before include "Total misrepresentation" , "Make grotesque" , "'Farce, parody (8)'" , "Grossly unfair representation" , "Take off" .)