Son and friend making a sortie (5)
I believe the answer is:
sally
'a sortie' is the definition.
('sally' can be a synonym of 'sortie')
'son and friend' is the wordplay.
'son' becomes 's'.
'and' says to put letters next to each other.
'friend' becomes 'ally' (I've seen this before).
's'+'ally'='SALLY'
'making' acts as a link.
(Other definitions for sally that I've seen before include "Witty riposte" , "Sarah might make a witty remark about the willow" , "Retort - Gracie Fields song" , "excursion" , "Sortie; witty retort" .)