noun

• (countable) An understanding between entities to follow a specific course of conduct.
  "to enter an agreement"
• (uncountable) 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."
• (uncountable, law) A legally binding contract enforceable in a court of law.
• (uncountable, linguistics, 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.
  "Having clarified what we mean by ‘Personʼ and ‘Numberʼ, we can now return to our earlier observation that a finite I is inflected not only for Tense, but also for Agreement. More particularly, I inflects for Person and Number, and must ‘agreeʼ with its Subject, in the sense that the Person/Number features of I must match those of the Subject."