What part of speech is yearly?

"Yearly" can be two parts of speech, depending on its function in the sentence:

* Adjective: When describing something that happens or is done once a year, such as "a yearly checkup."

* Adverb: When modifying a verb, adjective, or another adverb to indicate frequency, such as "The magazine is published yearly."

So, the part of speech of "yearly" is determined by its usage in the sentence.