Son given powerful injection (4)
I believe the answer is:
shot
'injection' is the definition.
(I know that injection can be written as shot)
'son given powerful' is the wordplay.
'son' becomes 's' (genealogical abbreviation for son).
'given' means one lot of letters go next to another.
'powerful' becomes 'hot' (hot can mean powerful or pungent).
's'+'hot'='SHOT'
(Other definitions for shot that I've seen before include "Charge" , "Fired; turn" , "Wounded" , "Ruined; photograph" , "pop!" .)