Chance intrepid leader's missing (5)
I believe the answer is:
lucky
'missing' is the definition.
Both the answer and definition are adjectives. Maybe you can see an association between them that I can't see?
'chance intrepid leader's' is the wordplay.
'chance' becomes 'luck' (synonyms).
'intrepid leader' becomes 'y' (I can't justify this - if you can you should give a lot more credence to this answer).
'luck'+'y'='LUCKY'
Can you help me to learn more?
(Other definitions for lucky that I've seen before include "by chance" , "Auspicious" , "Bringing good fortune" , "Game where prizes are picked from a tub" , "'It is better to be born . . . . . than rich'" .)