IPA: /ˈswɪf.tli/
KK: /ˈswɪf(t)li/
In a quick or fast way; moving or happening with speed.
The cheetah ran swiftly across the plains to catch its prey.
Swiftly → It is formed from "swift" (from Old English *swift*, meaning quick or fast) and "-ly" (meaning in a manner of). The word "swiftly" means in a quick or fast manner.
Think of 'swift' meaning quick, and remember that 'swiftly' describes doing something in a quick manner.