rapidly

As a letter s

is the letter s with a.

As an adverb rapidly is

with speed; in a rapid manner.

Mercurial is a related term of rapidly.

As a noun mercurial

is (obsolete) any of the plants known as mercury.

As an adjective mercurial

is (often capitalized, see (mercurial)) pertaining to the planet mercury.

As an adverb rapidly is

with speed; in a rapid manner.

Fleet is a related term of rapidly.

As a proper noun fleet

is the stream that ran where fleet street now runs.

As an adverb rapidly is

with speed; in a rapid manner.

Speedy is a related term of rapidly.

As an adjective speedy

is rapid; swift.

As an adverb rapidly is

with speed; in a rapid manner.

As a noun swiftness

is the state of being swift.

As an adverb rapidly is

with speed; in a rapid manner.

As an adverb rapidly

is with speed; in a rapid manner.

As an adjective undefined is

lacking a definition or value.

As adverbs the difference between rapidly and heavily

is that rapidly is with speed; in a rapid manner while heavily is in a heavy manner.

As a noun rapidness

is the characteristic of being rapid.

As an adverb rapidly is

with speed; in a rapid manner.

As adverbs the difference between firmly and rapidly

is that firmly is in a firm or definite or strong manner while rapidly is with speed; in a rapid manner.

As adverbs the difference between regularly and rapidly

is that regularly is with constant frequency or pattern while rapidly is with speed; in a rapid manner.