Rima
WordNet
noun
(1) A narrow elongated opening or fissure between two symmetrical parts
WiktionaryText
Noun
- A cleft or gap between two symmetrical parts, particularly between the vocal folds.
- A crack or fissure on a lunar or planetary surface; a rille.
- 2006, What's Up 2006: 365 Days of Skywatching http://books.google.com/books?id=tLUFJ53HG8sC, page 128:
- Look for three prominent interior craters, as well as an ancient rima falling near the shadow's edge.