* Adjective: This is the most common usage. It means "absolute, complete, or extreme," as in "The room was painted a stark white."
* Adverb: While less common, it can modify an adjective or another adverb, meaning "completely" or "utterly," as in "The room was starkly white."
* Noun: It can be used to refer to a type of wild pear tree, though this is quite specialized.
To determine which part of speech "stark" is, you need to look at how it's used in the sentence.