Not so well (5)

I believe the answer is:

worse

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

'not so well' is the definition.
Both the answer and definition are adjectives. Maybe you can see an association between them that I can't see?

This is the entire clue.

Can you help me to learn more?

(Other definitions for worse that I've seen before include "Bad to a greater degree" , "More serious" , "Of poorer quality" , "More awful or unwell" , "Opposite of better" .)

I've seen this clue in The Telegraph and The Guardian.

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