Stupid alien seen in coppice (7)
I believe the answer is:
thicket
'coppice' is the definition.
(I know that coppice can be written as thicket)
'stupid alien' is the wordplay.
'stupid' becomes 'thick' (similar in meaning).
'alien' becomes 'et' (extra terrestrial).
'thick'+'et'='THICKET'
'seen in' is the link.
(Other definitions for thicket that I've seen before include "Dense group of trees or bushes" , "A patch of shrubs and small trees" , "Mass of shrubs and bushes growing close together" , "Wood" , "Dense growth of bushes" .)