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. Note that in this sense words beginning with under often have counterparts beginning with over-: overcharge, overestimate.
