A very thin ridge of rock.
{{quote-text|en|year=2004|author=Richard Fortey|title=The Earth|page=88|publisher=Folio Society|year_published=2011
bone (of a fish), fishbone
edge (of an object); ridge, crest (of mountain)
groin (of vault)
bridge of nose
beard (of rye, barley etc.); awn
edge