About a clergyman, a wager is of military significance! (6)
I believe the answer is:
brevet
'of military significance' is the definition.
The definition suggests a singular noun which matches the answer.
'about a clergyman a wager' is the wordplay.
'about' is an insertion indicator.
'a clergyman' becomes 'rev' (short for reverend).
'a wager' becomes 'bet' ('bet' can be a synonym of 'wager').
'rev' inserted inside 'bet' is 'BREVET'.
'is' acts as a link.
Can you help me to learn more?
(Other definitions for brevet that I've seen before include "document" , "(Former) military commission" .)