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1530s, "action of coming together," from Medieval Latin associationem (nominative associatio), noun of action from past participle stem of associare (see associate). Meaning "a body of persons with a common purpose" is from 1650s. Meaning "mental connection" is from 1680s; that of "quality or thing called to mind by something else" is from 1810.
association as·so·ci·a·tion (ə-sō'sē-ā'shən, -shē-)
A connection of persons, things, or ideas by some common factor; union.
A functional connection of two ideas, events, or psychological phenomena established through learning or experience.