Labels men as fickle (5)
I believe the answer is:
names
'labels' is the definition.
(naming is a kind of labelling)
'men as fickle' is the wordplay.
'fickle' is an anagram indicator.
'men'+'as'='menas'
'menas' with letters rearranged gives 'NAMES'.
(Other definitions for names that I've seen before include "identification" , "Heroes" , "Paul, Pat, John" , "People and things are known by them" , "Appellations or identifiers" .)