fast, rapid, swift, fleet, speedy, quick, hasty, expeditious
These adjectives refer to something marked by great speed. Fast and rapid are often used interchangeably, though fast is more often applied to the person or thing in motion, and rapid, to the activity or movement involved: a fast runner; rapid strides. Swift suggests smoothness and sureness of movement (a swift current), and fleet, lightness of movement (The cheetah is the fleetest of animals). Speedy refers to velocity (a speedy train) or to promptness or hurry (a speedy resolution to the problem). Quick most often applies to what takes little time or to what is prompt: a quick snack; your quick reaction. Hasty implies hurried action (a hasty visit) and often a lack of care or thought (regretted the hasty decision). Expeditious suggests rapid efficiency: sent the package by the most expeditious means.
[AHD4] (italics added)
