These words refer to speed of movement. While quick can apply widely, it often refers less to rate of motion than to the suddenness or brief duration of a single action: a quick leap; a quick response to my question; The hand is quicker than the eye. It can apply also to a readiness to act: quick to take offence. When it indicates something of short duration, it often implies haste: He ate a quick breakfast and rushed off to work. While fast , too, can apply in a wide variety of ways, it is more apt than quick for referring to something in sustained motion, indicating here a high rate of speed or a capacity for such movement: a fast car; a fast getaway; You’re reading too fast for me to follow.

Rapid and swift are both more formal than the preceding pair and apply equally well to sudden or sustained movement: a rapid river; a rapid burst of machine-gun fire; a swift change of mood; a swift runner. Rapid has a special connotation relating to beneficial or advantageous speed; by contrast, both quick and fast can apply as well to catastrophic haste: a rapid recovery from his illness; rapid progress in slum clearance. A special connotation of swift relates to speed that is smooth, undisturbing, uninterrupted or seemingly effortless: a swift transition without hesitation or awkwardness; a communications network that was swift and silent in operation. Also, swift can give a lyrical overtone: the swift fading of autumn into winter.

Precipitate is the one word here that stresses dangerous, undesirable or foolhardy speed: two cars in a precipitate race through suburban traffic; a disguise that served him well in his precipitate flight from the concentration camp. Precipitous can often suggest falling or abrupt downward movement: the precipitous fall of share prices. Sometimes precipitous is erroneously used for precipitate. Precipitous means "very steep" and precipitate "violently hurried." But one might leave a room "precipitously " by jumping out of the window or falling downstairs.