What part if speech is sing?

"Sing" can be a few parts of speech depending on how it's used in a sentence:

* Verb: This is the most common use. Example: "The birds sing beautifully."

* Noun: It can be used to refer to the act of singing. Example: "Their sing was full of joy."

* Adjective: This is less common, but it can be used to describe something related to singing. Example: "They have a sing contest every year."

To determine the part of speech, you need to look at how the word is used in the sentence.