rap‧id‧ly W3 / ræpədli, ræpɪdli / 副词

very quickly and in a very short time :

The disease was spreading more rapidly than expected.

rapidly growing/changing/expanding etc

the rapidly changing world of technology

THESAURUS

quickly at a high speed or without taking much time : The stream was flowing quite quickly. | They quickly became friends.

fast at a high speed – used especially when talking about how something moves : You’re driving too fast! | He ran home as fast as he could.

quick spoken quickly – used in exclamations or in comparatives : Quick! There’s a mouse!

swiftly written quickly : The government acted swiftly. | She was surprised that he agreed so swiftly.

rapidly quickly – used especially about changes, increases, improvements etc : The population is growing rapidly. | a rapidly changing world

speedily quickly and therefore efficiently : All problems were speedily dealt with.

briskly quickly and energetically : He walked briskly back along the path.

at high/great speed at a very fast speed – used especially in technical descriptions : The molecules are travelling at great speed.

at a rapid rate especially written quickly – used about changes, increases, improvements etc : Internet shopping is growing at a rapid rate.

as quick as a flash/in a flash extremely quickly : As quick as a flash, I was back in my bed and under the covers.

like lightning moving extremely quickly : Like lightning, the cat darted under the bushes.

flat out especially British English at the fastest speed possible : The car was going flat out. | He was running flat out.