The Collaborative International Dictionary of English v.0.48:

Ingrown \In"grown`\, a.
   Having grown or appearing to grow into some other substance,
   especially a fingernail or toenail growing into the adjacent
   flesh.
   [1913 Webster +PJC]

   Ingrown toenail, a toenail whose edges have becoming
      imbedded in the adjacent flesh.
      [1913 Webster +PJC]

WordNet (r) 3.0 (2006):

ingrown toenail
    n 1: toenail having its free tip or edges embedded in the
         surrounding flesh [syn: ingrown toenail, onyxis]