* Preposition: This is the most common usage. It shows the location of something relative to something else.
* Example: "The cat is underneath the table."
* Adverb: It can also describe a verb, meaning "below" or "beneath."
* Example: "The treasure was buried underneath the oak tree."
* Adjective: Less common, but it can describe a noun, meaning "lower" or "below."
* Example: "The underneath part of the car was rusty."
To determine the part of speech, you need to consider the context of the sentence.