Agreement to finish every clue thus? (3)
I believe the answer is:
yes
'agreement' is the definition.
'finish every clue thus?' is the wordplay.
'finish' indicates one should take the final letters.
The last letters of 'every clue thus' are 'YES'.
'to' acts as a link.
(Other definitions for yes that I've seen before include "Agreed" , "Affirmative reply" , "Confirmation" , "Certainly!" , "One response to "will you marry me?"" .)