Why so terribly late coming in? That's rich! (7)
I believe the answer is:
wealthy
This might be a double definition.
'why so terribly late coming in?' is the first definition.
Both the answer and definition are adjectives. Maybe you can see a link between them that I don't see?
'rich' is the second definition.
(similar in meaning)
'that's' is the link.
Can you help me to learn more?
(Other definitions for wealthy that I've seen before include "Affluent" , "Rich and prosperous" .)