Rectangle (6)
I believe the answer is:
oblong
'rectangle' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for oblong that I've seen before include "Log on B (anag.)" , "Plane figure that deviates from a square by elongation" , "Elongated rectangle" , "Roughly rectangular" , "Oval" .)