Fool turned up in tank top (3)
I believe the answer is:
nit
'fool' is the definition.
(thesaurus)
'turned up in tank top' is the wordplay.
'turned up' is a reversal indicator.
'top' says to take the initial letters.
The initial letter of 'tank' is 't'.
'in' reversed gives 'ni'.
'ni'+'t'='NIT'
(Other definitions for nit that I've seen before include "Hair louse" , "Cause of much head-scratching" , "no egghead?" , "Egg; fool" , "Foolish person" .)