quickly
The Italian word 'rapidamente' is an adverb, similar to 'quickly' in English. It is used in sentences to modify verbs, giving them the quality of speed or swiftness. Because it is an adverb, it is mostly used along with verbs rather than nouns.
You need to walk rapidly to reach the bus.
In this example, the word 'rapidamente' is used to describe the speed of an action, walking, indicating it needs to be done quickly in order to reach the bus on time.
They are working rapidly to complete the project.
Here the word 'rapidamente' is used to describe the manner in which the subjects (they) are performing an action (working), indicating it's being done swiftly in order to complete a project.
She speaks rapidly when she's nervous.
In this sentence, 'rapidamente' is used to indicate the speed of a normally neutral action (speaking), indicating an increase in speed tied to an emotional state (nervousness).