Sudden advances made by son with friends (7)
I believe the answer is:
sallies
'sudden advances' is the definition.
The answer and definition can be both acts as well as being plural nouns.
Maybe you can see a link between them that I don't see?
'son with friends' is the wordplay.
'son' becomes 's'.
'with' means one lot of letters go next to another.
'friends' becomes 'allies' ('ally' can be a synonym of 'friend').
's'+'allies'='SALLIES'
'made by' is the link.
Can you help me to learn more?
(Other definitions for sallies that I've seen before include "Atacks or witty remarks" , "Attacks" , "Repartees" , "fighting charges" , "Ripostes" .)