Growth promoter, foreign one, cut imports (8)
I believe the answer is:
sunlight
'growth promoter' is the definition.
(sunlight helps things grow)
'foreign one cut imports' is the wordplay.
'foreign one' becomes 'un' (French for 'one').
'cut' becomes 'slight' (slight can mean a wound or cut).
'imports' means one lot of letters goes inside another (inserted letters are imported).
'un' placed into 'slight' is 'SUNLIGHT'.
(Other definitions for sunlight that I've seen before include "port?" , "Solar rays" , "Beams" , "Hustling under heavenly radiance" , "What's illuminating, naturally" .)