Let loose at the outset then relax (5)
I believe the answer is:
lease
'let' is the definition.
(as in to lease or let a building)
'loose at the outset then relax' is the wordplay.
'at the outset' says to take the initial letters.
'then' is a charade indicator (letters next to each other).
'relax' becomes 'ease' (I've seen this in other clues).
The first letter of 'loose' is 'l'.
'l'+'ease'='LEASE'
(Other definitions for lease that I've seen before include "Contract allowing use of a property" , "Let; rent" , "From legal document" , "Letting contract" , "Contract for, say, use of building" .)