Allow to hire (3)
I believe the answer is:
let
I believe this is a double definition.
'allow' is the first definition.
('let' can be a synonym of 'allow')
'hire' is the second definition.
(thesaurus)
'to' is the link.
(Other definitions for let that I've seen before include "Rent out (property)" , "& 15 Triple (anag.)" , "inefficient service" , "Disappoint or fail to support - ... down" , "Service that must be repeated" .)