Agreement to pay for a year (6)
I believe the answer is:
treaty
'agreement' is the definition.
(treaty is a kind of agreement)
'pay for a year' is the wordplay.
'pay for' becomes 'treat' (I've seen this before).
'a year' becomes 'y'.
'treat'+'y'='TREATY'
'to' is the link.
(Other definitions for treaty that I've seen before include "alliance" , "Ratified agreement between states" , "Formal pact" , "Negotiation" , "Formal agreement between two or more countries" .)