Departed class with hesitation (6)
I believe the answer is:
former
'departed' is the definition.
(thesaurus)
'class with hesitation' is the wordplay.
'class' becomes 'form' (synonyms).
'with' means one lot of letters go next to another.
'hesitation' becomes 'er' (sound made while hesitating - um, er).
'form'+'er'='FORMER'
(Other definitions for former that I've seen before include "Of an earlier period, or mentioned before another" , "Ex-" , "The first of two, earlier" , "late" , "The first mention of the two" .)