Resolving timeless dispute can be positive (6)

I believe the answer is:

upside

I'm a little stuck... Click here to teach me more about this clue!

'positive' is the definition.
(an upside is a positive aspect of something)

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for upside that I've seen before include "Positive aspect of a situation" , "advantage" , "Favourable aspect" , "Top surface of something" .)

I've seen this clue in The Guardian.

Want a hint initially instead of a full solution? Install my app