The quality of being agreeable; the state of being pleasant, willing to agree, or suited to one's needs.
From agreeable (pleasant, willing to consent) + -ity (suffix forming abstract nouns). Agreeable comes from agree + -able (capable of being), ultimately from Latin 'ad gratum' (to pleasure).
In personality psychology, 'agreeableness' is one of the Big Five traits measured in personality tests, but the older term 'agreeability' appears more in philosophy and older texts. It captures something slightly different—less about personality and more about the actual quality of harmony.
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