Definition of rapid adjective from the Oxford Advanced Learner's Dictionary

rapid

adjective

ˈræpɪd

ˈræpɪd

1 [usually before noun] happening in a short period of timerapid change/expansion/growtha rapid rise/decline in salesThe patient made a rapid recovery.

2 done or happening very quicklya rapid pulse/heartbeatThe guard fired four shots in rapid succession.The disease is spreading at a rapid rate.rapidity

rəˈpɪdəti

rəˈpɪdəti

noun [uncountable]the rapidity of economic growthThe disease is spreading with alarming rapidity.

rapidly

ˈræpɪdli

ˈræpɪdli

adverba rapidly growing economyCrime figures are rising rapidly.

Usage note: fast / quick / rapidThese adjectives are frequently used with the following nouns:

fast ~	quick ~	rapid ~
car	glance	change
train	look	growth
bowler	reply	increase
pace	decision	decline
lane	way	progress

Fast is used especially to describe a person or thing that moves or is able to move at great speed.Quick is more often used to describe something that is done in a short time or without delay.Rapid, swift and speedy are more formal words.Rapid is most commonly used to describe the speed at which something changes. It is not used to describe the speed at which something moves or is done: a rapid train ◇ We had a rapid coffee.Swift usually describes something that happens or is done quickly and immediately: a swift decision ◇ The government took swift action.Speedy has a similar meaning: a speedy recovery. It is used less often to talk about the speed at which something moves: a speedy car.For the use of fast and quick as adverbs, see the usage note at quick.