What part of speech is groan?

"Groan" can be either a verb or a noun, depending on how it's used in a sentence.

Verb: When "groan" describes an action, it's a verb.

* Example: The old floorboards groaned under the weight of the heavy furniture.

Noun: When "groan" refers to the sound itself, it's a noun.

* Example: A groan of despair escaped her lips.