Ornamental plant favoured on college area (7)
I believe the answer is:
petunia
'ornamental plant' is the definition.
(I know that petunia is a type of ornamental plant)
'favoured on college area' is the wordplay.
'favoured' becomes 'pet' (as in a pet project).
'on' says to put letters next to each other (in a down clue, letters appear on others).
'college' becomes 'uni' (short for university).
'area' becomes 'a' (maths abbreviation).
'pet'+'uni'+'a'='PETUNIA'
(Other definitions for petunia that I've seen before include "Popular plant for baskets" , "Common bedding plant" , "Flower much used in hanging baskets" , "Common garden 13 across" , "Garden plant with large funnel-shaped flower" .)