Is it ensure, insure, or assure?
(from the Greek meaning "known life"), condition of life in which only known kinds of organisms are present. Gnotobiotic organisms are of two major types: germfree, that is, free of all known contaminants; and gnotophoric, bearing a single known contaminant, usually administered as part of an experiment. The term "germfree," however, is often used loosely to indicate all organisms cultivated under laboratory conditions in the absence of any other detectable species or in the presence of species known by the investigator to be present. Gnotobiotics has made possible the study of many biological functions unhampered by normal body contamination. Its techniques are now widely used in producing disease-free laboratory and stock animals, in sterilization of space vehicles, and in the study of the origin of life. See also germfree life.