agreeableness has 2 distinct synonyms spread across 2 of its 2 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 disagreeableness.
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.
pleasantness resulting from agreeable conditions
“a well trained staff saw to the agreeableness of our accommodations”
a temperamental disposition to be agreeable
Synonyms, antonyms and the broader and narrower relations for agreeableness come from Princeton University’s WordNet. Full sources and licences.