One side that's correct (5)
I believe the answer is:
right
I believe this is a double definition.
'one side' is the first definition.
(I've seen this before)
'correct' is the second definition.
(right can mean correct)
'that's' is the link.
(Other definitions for right that I've seen before include "Girth (anag)" , "Accurate" , "Correct; political wing" , "Correct; appropriate" , "Genuine" .)