Tail of rook found in tree (6)
I believe the answer is:
breech
'tail' is the definition.
(thesaurus)
'rook found in tree' is the wordplay.
'rook' becomes 'R' (chess abbreviation).
'found in' indicates putting letters inside.
'tree' becomes 'beech' (beech tree is a kind of tree).
'r' inserted into 'beech' is 'BREECH'.
'of' is the link.
(Other definitions for breech that I've seen before include "One's behind" , "Prat" , "Rear part of rifle" , "Back end of a gun barrel" , "Lower part of a gun" .)