What is the difference between “quick“, “quickly” and “fast” in English?
These 3 words are related to speed or time. They are similar but there are a few important differences. Let’s look at each one in more detail.
Quick
“quick” is an English adjective. It gives us more information about a noun (person, place or thing).
Meaning: “quick” describes something that happens in a short time.
Examples:
We had a quick drink before going home.
Let’s have a quick meeting to discuss recruitment.
Jane gave Mark a quick kiss.
Quickly
“quickly” is an adverb and it therefore gives us more information about a verb.
There are two definitions and uses of “quickly“:
1) At high speed
Examples:
I don’t understand. You’re talking too quickly.
He’s running quickly.
2) After a short time
Examples:
He replied quickly to my letter.
The ambulance arrived quickly after the accident.
Fast
“fast” is an adjective and adverb.
Fast as an adjective
As an adjective, the meaning is to describe a noun (something or someone) that moves at high speed.
Example: I have a fast car.
Fast as an adjective
“fast” is an irregular adverb. It describes a verb (action) that is happening at high speed.
Example: He is walking fast.
Expressions with fast
fast food
Meaning: “fast food” is food that is prepared at high speed and in a short period of time.
Example: Fast food is bad for your health if you eat too much of it.
fast asleep
Meaning: To be completely asleep.
Example: The baby is fast asleep.
Common mistakes with “fast”
“fast” has the same spelling when it is an adjective and an adverb. We do not say “fastly” when it is an adverb.
Example:
He runs fast. 
He runs fastly. 
We use “quick” to describe something that takes a short time. We do not use “fast” to describe something that takes a short time.
Example:
I had a quick conversation with Jane yesterday.
I had a fast conversation with Jane yesterday.
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Marie says
Well explained.