Surpass son in away journey (8)
I believe the answer is:
outstrip
'surpass' is the definition.
('outstrip' can be a synonym of 'surpass')
'son in away journey' is the wordplay.
'son' becomes 's'.
'in' means one lot of letters goes inside another.
'away' becomes 'out' ('out' can be a synonym of 'away').
'journey' becomes 'trip' (trip is a kind of journey).
'out'+'trip'='outtrip'
's' put within 'outtrip' is 'OUTSTRIP'.
(Other definitions for outstrip that I've seen before include "Outrun or surpass" , "Surpass, do better than" , "Exceed in performance" , "eclipse" , "Surpass, overtake" .)