Unsettled round greenery, last rook departs (7)
I believe the answer is:
overdue
'unsettled' is the definition.
(I've seen this before)
'round greenery last rook departs' is the wordplay.
I cannot really understand how this works, but
'round' could be 'o' (round can mean a round object) and 'o' is found in the answer.
'rook' could be 'r' (chess abbreviation) and 'r' is found in the answer.
'departs' could be 'd' (common abbreviation e.g. train timetables) and 'd' is found within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for overdue that I've seen before include "Behindhand" , "Do revue after the appointed time" , "Not paid by the agreed time, late" , "Past the appointed date for payment" , "after the time specified" .)