Cover article supporting nut tree (7)
I believe the answer is:
sheathe
'cover' is the definition.
(sheathing is a kind of covering)
'article supporting nut tree' is the wordplay.
'article' becomes 'the' (the 'definite article' part of speech).
'supporting' says to put letters next to each other (in a down clue, some letters go below others).
'nut tree' becomes 'shea'.
'the' after 'shea' is 'SHEATHE'.
(Other definitions for sheathe that I've seen before include "Put (a sword) into case" , "Put (a sword) it its cover" , "Encase in protection" , "stow away safely" , "Put into scabbard" .)