Couple's fifty tattoos deteriorate over time (7)
I believe the answer is:
linkage
'time' is the definition.
Although both the answer and definition are singular nouns, I can't understand how they can define each other.
'couple's fifty tattoos deteriorate' is the wordplay.
'couple's fifty' becomes 'l' (I can't explain this - if you can you should give a lot more credence to this answer).
'tattoos' becomes 'ink' (I've seen this in another clue).
'deteriorate' becomes 'age' (ageing is a kind of deteriorating).
'l'+'ink'+'age'='LINKAGE'
'over' acts as a link.
Can you help me to learn more?
(Other definitions for linkage that I've seen before include "where the join is" , "System of connections" , "Connection, coupling" , "Connection, bond" , "Part of mechanism" .)