Kidnap missing leader? Certainly (5)
I believe the answer is:
natch
'certainly' is the definition.
(I've seen this in another clue)
'kidnap missing leader?' is the wordplay.
'kidnap' becomes 'snatch' (synonyms).
'missing leader?' means to remove the first letter (leader meaning lead letter).
'snatch' with its initial letter removed is 'NATCH'.
(Other definitions for natch that I've seen before include "Of course, commonly < , behind" , "a display of Indian dancing" , "obviously" , "Of course! (US sl.)" .)