What part of speech is overdue?

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

Adjective:

* Example: The library book is overdue.

* In this example, "overdue" modifies the noun "book" and describes its state.

Adverb:

* Example: The payment is overdue.

* Here, "overdue" modifies the verb "is" and describes the timeliness of the payment.

It's important to consider the context to determine the correct part of speech.