Lawyer's beginning to relax tenancy contract (5)
I believe the answer is:
lease
'tenancy contract' is the definition.
(I've seen this before)
'lawyer's beginning to relax' is the wordplay.
'beginning to' indicates taking the first letters.
'relax' becomes 'ease' (I've seen this before).
The first letter of 'lawyers' is 'l'.
'l'+'ease'='LEASE'
(Other definitions for lease that I've seen before include "Rent -- easel (anag)" , "Contract of tenure" , "Summer's has too short a date (Shak.)" , "Let; rent" , "Renting contract" .)