Is the word louder an adverb or adjective?

"Louder" can be both an adverb and an adjective, depending on its role in the sentence.

Adverb: When it modifies a verb, adjective, or another adverb, describing how something is done or to what degree.

* Example: "The music was playing louder than before." (modifies the verb "playing")

Adjective: When it describes a noun, indicating a higher level of sound.

* Example: "The louder sound startled me." (describes the noun "sound")

To determine its part of speech, consider what it modifies in the sentence.