1 [noncount] a : the act of agreeing ▪ Any changes to the plan require the agreement of everyone involved. ▪ We were surprised by his agreement to participate. [=we were surprised that he agreed to participate] ▪ She nodded her head in agreement. [=to show that she agreed] b : a situation in which people share the same opinion : a situation in which people agree ▪ There is wide/widespread/universal agreement on this issue. ▪ Everyone seems to be in agreement [=seems to agree] about/on the need for reform, but there is much disagreement about how to achieve it. ▪ They have been unable to reach agreement about how to achieve reform.
2 [count] a : an arrangement, contract, etc., by which people agree about what is to be done ▪ I thought we had an agreement. ▪ a formal/contractual agreement ▪ Their agreement expires next year. ▪ He has to return the property under the terms of an agreement he has with the original owner. ▪ a peace agreement ▪ a trade agreement ▪ They have come to an agreement. = They have reached an agreement. b : a written record of such an agreement ▪ He signed an agreement to buy the property. —see also gentleman's agreement
3 [noncount] grammar : the fact or state of being alike in gender, number, case, or person : the fact or state of agreeing grammatically ▪ The subject and the verb need to be in agreement (with each other).