Candid leader in front line (5)
I believe the answer is:
frank
'candid' is the definition.
(I know that candid can be written as frank)
'leader in front line' is the wordplay.
'leader in' suggests taking the first letters.
'line' becomes 'rank' (rank is a kind of line).
The first letter of 'front' is 'f'.
'f'+'rank'='FRANK'
(Other definitions for frank that I've seen before include "Blunt; honest" , "Open" , "Anne ---, diarist" , "Old German" , "stamp" .)