Let loose, initially, on facility (5)
I believe the answer is:
lease
'let' is the definition.
('lease' can be a synonym of 'let')
'loose initially on facility' is the wordplay.
'initially' says to take the initial letters.
'on' says to put letters next to each other.
'facility' becomes 'ease' (I've seen this before).
The initial letter of 'loose' is 'l'.
'l'+'ease'='LEASE'
(Other definitions for lease that I've seen before include "Summer's has too short a date (Shak.)" , "Contract for, say, use of building" , "Let out, hire" , "Letting contract" , "Ghost" .)