Animal concealed round middle of greenwood (4)
I believe the answer is:
hind
'animal' is the definition.
(I've seen this before)
'concealed round middle of greenwood' is the wordplay.
'concealed' becomes 'hid' ('hide' can be a synonym of 'conceal').
'round' is an insertion indicator.
'middle of' says to take the centre.
The middle of 'greenwood' is 'n'.
'hid' enclosing 'n' is 'HIND'.
(Other definitions for hind that I've seen before include "A female deer, situated at the back?" , "Be in front of this farm-worker" , "posterior" , "Rear - animal" , "Rear - female deer" .)