Majestic advance on tree (7)
I believe the answer is:
sublime
'majestic' is the definition.
(I've seen this in another clue)
'advance on tree' is the wordplay.
'advance' becomes 'sub' (I've seen this in other clues).
'on' says to put letters next to each other.
'tree' becomes 'lime tree' (type of tree).
'sub'+'lime'='SUBLIME'
(Other definitions for sublime that I've seen before include "Of great excellence or beauty, awe-inspiring" , "Majestic" , "Heavenly" , "Of the most exalted or noble kind" , "Exalted; awesome" .)