Not left straight (5)
I believe the answer is:
right
This clue is a double definition.
'not left' is the first definition.
('right' is the opposite to 'left')
'straight' is the second definition.
(similar in meaning)
(Other definitions for right that I've seen before include "Fair or just" , "Not left" , "Starboard side" , "A person is entitled to it" , "Just - correct - title" .)