Contract permitting relaxation, at length (5)
I believe the answer is:
lease
'contract' is the definition.
(I know that lease is a type of contract)
'relaxation at length' is the wordplay.
'relaxation' becomes 'ease' (synonyms).
'at' means one lot of letters go next to another (I've seen this in other clues).
'length' becomes 'l' (abbreviation in geometry).
'ease' put after 'l' is 'LEASE'.
'permitting' acts as a link.
I am not very happy about this link. It may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for lease that I've seen before include "Contract for, say, use of building" , "Term of a rental contract" , "Renting contract" , "Contract allowing use of a property" , "Rent (a property)" .)