* Preposition: This is the most common usage, indicating location or position.
* Example: The book is under the table.
* Adverb: Describing a verb, adjective, or another adverb, often indicating a lower position.
* Example: The plane flew under the clouds.
* Adjective: Describing something as being below a particular level.
* Example: The under side of the table is dusty.
To determine the part of speech, you need to look at the context of the sentence.