The word "under" is a preposition used to indicate a position below or beneath something. It can refer to a physical location, where one thing is directly below another, or it can be used in a more abstract sense, such as to indicate a state or condition that is subordinate or less than something else.
The word "under" comes from Old English "under," which is of Germanic origin. It has cognates in Old Norse "undr," meaning "under," and in German "unter."