Meaning of endosymbiosis

en•do•sym•bi•o•sis

Pronunciation: (en"dō-sim"bē-ō'sis, -bī-), [key]
— n. Biol.
  1. symbiosis in which one symbiont lives within the body of the other.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.