agree has 15 distinct synonyms spread across 3 of its 7 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 disagree.
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.
consent or assent to a condition, or agree to do something
“She agreed to all my conditions”
be agreeable or suitable
“White wine doesn't agree with me”
achieve harmony of opinion, feeling, or purpose
“No two of my colleagues would agree on whom to elect chairman”
1 of the 7 recorded senses carries no synonym, antonym or related term, so it is not shown above. Every sense, with its definition and examples, is on the full entry for agree.
Synonyms, antonyms and the broader and narrower relations for agree come from Princeton University’s WordNet. Full sources and licences.