An adjective describes or modifies a noun, telling you what something is like. An adverb modifies a verb, an adjective, or another adverb, telling you how, when, where or to what degree something happens. In "the red car," red is an adjective; in "she ran quickly," quickly is an adverb.
The core difference
An adjective modifies a noun, while an adverb modifies a verb, an adjective, or another adverb.
- adjective — a word that describes or modifies a noun: in "the red car," "red" is the adjective.
- adverb — a word that modifies a verb, an adjective or another adverb, showing how, when, where or to what degree: in "she ran quickly," the adverb is "quickly".
How to tell them apart
Ask what the word is attached to. If it's sitting next to a noun and describing it — a red car, a happy dog — it's an adjective. If it's attached to a verb and describing how, when, where or to what degree the action happens — ran quickly, arrived yesterday, waited here — it's an adverb.
Many adverbs end in -ly, which is a handy but not foolproof hint ("friendly" is an adjective, for instance), so it's worth checking what the word is actually modifying rather than relying on the ending alone.
