niche in WordNet English dictionary

1. a small concavity
   recess  recession  niche  corner 
   
2. (ecology) the status of an organism within its environment and community (affecting its survival as a species)
   niche  ecological niche 
   
3. an enclosure that is set back or indented
   recess  niche 
   
4. a position particularly well suited to the person who occupies it
   "he found his niche in the academic world"
   niche