Just horrible, not fine (8)

I believe the answer is:

rightful

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

'just' is the definition.
(similar in meaning)

I cannot understand how the remainder of the clue works.

(Other definitions for rightful that I've seen before include "Legitimate - deserved" , "Having a legally established claim" , "Lawful" , "Legitimately claimed" , "According to justice" .)

I've seen this clue in The Sunday Times.

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