One that contracts to a smaller extent, even extending at the edges (6)
I believe the answer is:
lessee
'one that contracts to a smaller extent even extending at the edges' is the definition.
Although both the answer and definition are singular nouns, I cannot see how they can define each other.
'one that contracts to a smaller extent even' is the wordplay.
'one that contracts' means to remove the last letter (I've seen 'contracted' mean this (to contract is to shorten)).
'to a smaller extent' becomes 'less' (I've seen this in another clue).
'even' becomes 'e'en' (synonyms).
'less'+'een'='lesseen'
'lesseen' with its final letter taken away is 'LESSEE'.
Can you help me to learn more?
(Other definitions for lessee that I've seen before include "Tenant with a contract" , "The one taking out lease" , "Person who holds building on contract for specified time" , "I have to deal with letter" , "One holds a lease" .)