agreement has 5 distinct synonyms spread across 5 of its 6 senses. Each sense below keeps its own list, because a synonym belongs to a meaning and not to a word: swapping one sense's substitute into another sense's sentence is how a thesaurus makes writing worse. Its one recorded opposite is disagreement.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
the statement (oral or written) of an exchange of promises
“they had an agreement that they would not interfere in each other's business”
compatibility of observations
“there was no agreement between theory and measurement”
harmony of people's opinions or actions or characters
“the two parties were in agreement”
the thing arranged or agreed to
“they made arrangements to meet in Chicago”
the verbal act of agreeing
Synonyms, antonyms and the broader and narrower relations for agreement come from Princeton University’s WordNet. Full sources and licences.