Columbia Encyclopedia World Factbook American Heritage Coll. A Practical and Authoritative Guide to Contemporary English. The prefix under-, which can be traced back to Old English, has essentially the same meaning as the preposition under. For example, in words such as underbelly, undercurrent, underlie, and undershirt, under- denotes a position beneath or below. Under- also frequently conveys incompleteness or falling below a certain standard.
Some examples are undercharge, underdeveloped, underestimate, and underfeed.
Many English words beginning with uni- were formed in Latin. The majority of new words with uni-, such as unicellular, unicycle, unilateral, and univalent, are from the 19th century. Its use dates back to Old English. Other examples are outward, forward, backward, upward, downward, earthward, homeward, northward, southward, eastward, and westward. The suffix -ward forms adjectives and adverbs.