The word "deep" generally refers to something that has a considerable distance from the top to the bottom or from the surface to the interior. It can describe physical objects, like a deep pool of water or a deep hole, as well as abstract concepts, such as deep thoughts or deep feelings, indicating complex or significant levels of understanding or emotion.
The word "deep" originates from Old English "deop," which means "profound, intense, or the lower part of." Its roots can be traced back to Proto-Germanic "deupaz" and further to Proto-Indo-European "d(e)u̯b-", which means "to sink" or "to be low."