Agreement

noun

1. An understanding between entities to follow a specific course of conduct.

   "to enter an agreement;  the UK and US negotiators nearing agreement;  he nodded his agreement."

2. A state whereby several parties share a view or opinion; the state of not contradicting one another.

   "The results of my experiment are in agreement with those of Michelson and with the law of General Relativity."

3. A legally binding contract enforceable in a court of law.
4. (grammar) Rules that exist in many languages that force some parts of a sentence to be used or inflected differently depending on certain attributes of other parts.
5. (chiefly in the plural) An agreeable quality.