What part of speech is tasteless?

"Tasteless" can be either an adjective or an adverb, depending on how it's used in a sentence.

As an adjective: It describes a noun, meaning lacking flavor or having an unpleasant flavor.

* Example: "The soup was tasteless."

As an adverb: It modifies a verb, adjective, or another adverb, meaning "in a way that lacks taste or is offensive."

* Example: "He spoke tastelessly about the accident."