Thick can be an adjective, a noun and an adverb.
Adjective: e.g. heavy in build.
Noun: The thickest part of something.
Adverb: In a thick manner.
A word used to describe a noun is an adjective; a word used to describe, or modify, a verb or an adjective is an adverb. Thick is usually an adjective; thickly would be the adverb form. You look at the usage of a word in a sentence to find its "part of speech."
The part of speech for this particular word is a noun.
The part of speech that the word my is used as is an adjective.
The part of speech for the word "boulevard" is a noun.
The part of speech for the word civilian is English grammar.
The word speech is a noun.
It is not ANY part of speech, there is no such English word as "stroobly".
The part of speech for this particular word is a noun.
The word speech is a noun.
The word speech is a noun.
The word speech is a noun.
A suffix changes a word's part of speech. For example, the word 'happy' is an adjective. But when you add a suffix, which is an ending, it can change the part of speech. Happily is an adverb. Happiness is a noun.