These words refer to rapid motion or to the immediate execution of a task. Speed , swiftness and velocity are the most general of these, with speed the least and velocity the most formal. Speed can be used of any rapid and continuing motion: The speed of the horses along the track was simply amazing. It is especially appropriate in referring to vehicles, machines or inanimate projectiles: Speed and more speed is what the hot-rod enthusiast is after. It can, of course, refer to the rate of motion and not necessarily to fast motion at all: The tortoise crept along at an agonizingly slow speed . Velocity has only scientific or technical uses and would pretentious in other situations. It can refer to rapid, continuing motion, but is more often used for rate of motion.

• The rocket attained an orbit of astounding velocity ; The velocity of sound falls far short of the speed of light.

Swiftness does not apply to rate of motion but is otherwise almost interchangeable with speed . It is slightly more formal and would be used less of vehicles and machines than for living things. It may have a lyrical or poetic quality that is by no means necessarily trite or stilted.

• The wild ducks streamed across the sky with a swiftness that dazzled every onlooker; A ballet dancer must possess both strength and swiftness .

Unlike speed , swiftness often refers also to a very brief interval: the swiftness with which she answered my question.

Haste and hurry both refer to a rushed manner of behaviour. Haste is equally appropriate to formal and informal contexts and tends to imply the ineffective performance of a task, as in the motto, haste makes waste. When this overtone is absent, an extremely brief or partial action is still implied: Forgive the haste with which this note is written; I will send a long letter shortly. Hurry is more informal than haste , but otherwise similar in its possible overtone of ineffectiveness: How can you avoid mistakes when you’re in such a hurry ?

Dispatch is much more formal than either haste or hurry and is opposed to them in implying rapid action that is both efficient and thorough. It also suggests the total completion of a task.

• Whether could he find a secretary who took dictation with such dispatch ?; The dispatch with which she finished the leftovers astonished everyone else at the table.

Promptness , while slightly less formal than dispatch , also suggests an efficient swiftness ; it is restricted, however, to refer to punctuality or to the accomplishment of a task in a given time.

• Haste simply cannot make up for your lack of promptness; Despite the fall of two governments, the war correspondent turned in his report with his usual promptness .

It can refer also to the briefness of an interval of time: He expected her to agree to his request, but the promptness of her reply delighted him.

Alacrity and celerity are the most formal of these words and apply more to readiness in a person’s attitude than to speed of motion. Alacrity implies a cheerful willingness to act: The waiter’s alacrity in greeting us and finding us a table did not match the speed with which he delivered the food we ordered. Celerity also may be used in this way but, unlike alacrity , it can apply simply to the speed of a continuing motion: The ungainly look of an ostrich is belied by the celerity with which it can outdistance its more graceful enemies. Both words may tend to sound pretentious or stilted.