The Collaborative International Dictionary of English v.0.48:

Pothole \Pot"hole`\, n.
   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.
   [1913 Webster]

WordNet (r) 3.0 (2006):

pothole
    n 1: a pit or hole produced by wear or weathering (especially in
         a road surface) [syn: pothole, chuckhole]