pothole

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A hole or pit, especially one in a road surface.
• noun A deep round hole worn in rock by loose stones whirling in strong rapids or waterfalls.
• noun Western US A place filled with mud or quicksand that is a hazard to cattle.

from The Century Dictionary.

• To produce in (a solid rock mass) a hole by the action of stones and silt whirled around in an eddy of water. The effect of such action is to produce a deep cylindrical hole, called a well, or a hollowed cavity, called a pot-hole, or, in rare cases, a very large and deep, more or less cylindrical and hollowed cavern, called a giants' kettle or cauldron.
• noun A cavity more or less nearly cylindrical in form, and from a few inches to several feet in depth and diameter, made by an eddying current of water, which causes a stone or a collection of detrital material to revolve and thus wear away the rock with which it is in contact.

from the GNU version of the Collaborative International Dictionary of English.

• noun A circular hole formed in the rocky beds of rivers by the grinding action of stones or gravel whirled round by the water in what was at first a natural depression of the rock.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun archaeology A pit resulting from unauthorized excavation by treasure hunters or vandals.
• noun A shallow pit or other edged depression in a road's surface, especially when caused by erosion by weather or traffic.
• noun A pit formed in the bed of a turbulent stream.
• noun geology A vertical cave system, often found in limestone.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a pit or hole produced by wear or weathering (especially in a road surface)