Figure almost left behind old college (7)
I believe the answer is:
polygon
'figure' is the definition.
(polygon is a kind of figure)
'almost left behind old college' is the wordplay.
'almost' means to remove the last letter (most of the word but not all of it).
'left' becomes 'gone' (go can mean to leave).
'behind' is a charade indicator (letters next to each other).
'old college' becomes 'poly' (polytechnic).
'gone' with its last letter taken away is 'gon'.
'gon' after 'poly' is 'POLYGON'.
(Other definitions for polygon that I've seen before include "shape" , "Figure with many sides" , "Closed plane figure with three or more straight sides" , "Plane figure with a number of straight sides" , "Straight-sided figure" .)