Jests go stale in time (8)
I believe the answer is:
badinage
'jests go' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
'stale in time' is the wordplay.
'stale' becomes 'bad' (similar in meaning).
'time' becomes 'age' (an age is a period of time).
'bad'+'in'+'age'='BADINAGE'
Can you help me to learn more?
(Other definitions for badinage that I've seen before include "joking" , "Beg Diana with good-humoured teasing" , "A big Dane given to banter" , "Wordplay" , "Frivolous backchat" .)