Worry stops attempt to reach agreement (6)
I believe the answer is:
treaty
'agreement' is the definition.
(I know that agreement can be written as treaty)
'worry stops attempt' is the wordplay.
'worry' becomes 'eat' (something worrying may eat someone up).
'stops' indicates putting letters inside (stopping can mean blocking a gap).
'attempt' becomes 'try' (synonyms).
'eat' put inside 'try' is 'TREATY'.
'to reach' is the link.
(Other definitions for treaty that I've seen before include "Contract between states" , "Covenant" , "Deal?" , "Pact, accord between states" , "Formal agreement between governments" .)