What is that word that sounds like "assent" in No Game No Life?
The only word that closely resembles the word you're asking for is "Aschente". It's pronounced more or less like: "A-shen-te".

It means one pledges to the ten 'rules' made, and placed by the one true god Tet of Disboard. They state it at the start of every game that uses the ten rules.

(I've linked more about the ten pledges and such in the link above)