接頭辞af-はad-と同じ、行く。-fairはフランス語のfactの変化形。
'Tis manife?tly contrary to the Law of Nature, that one Woman ?hould cohabit or have an Affair of Love with more than one Man at the ?ame time. ["Pufendorf's Law of Nature and Nations," transl. J. Spavan, London, 1716]
Thus, in our dialect, a vicious man is a man of pleasure, a sharper is one that plays the whole game, a lady is said to have an affair, a gentleman to be a gallant, a rogue in business to be one that knows the world. By this means, we have no such things as sots, debauchees, whores, rogues, or the like, in the beau monde, who may enjoy their vices without incurring disagreeable appellations. [George Berkeley, "Alciphron or the Minute Philosopher," 1732]