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Adverbs express the way actions take place. To some extent, they are similar to adjectives but they refer to verbs instead of nouns.
In the sentence “What a wonderfully coloured dress!”, the word “Wonderfully”, which is an adverb, expresses the way the dress is coloured.)
But if you say “Your dress is wonderful.”, then the word “wonderful” refers to the name “dress”, therefore it is an adjective, not an adverb.
Often adverbs end with the suffix “ly” (beautifully, extremely, wonderfully, etc.) but it is not a rule, in fact, there are many words that can be both adverbs and adjectives.
For example the word “fast” can be both an adjective or an adverb:
“This car is very fast.” (adjective)
“The car was going very fast.” (adverb)
In the first sentence the word “fast” refers to the noun “car”. In the second sentence the word “fast” refers to the verb “to go”.
Adverbs may also refer to adjectives or other adverbs, as in the expression “very fast” in which the word “very” is an adverb and “fast” is an adjective.