observer
ob.serv.er \*b-'z*r-v*r\ n : one that observes : as : a representative sent to observe but not participate officially in a ga thering : one who accompanies the pilot of an airplane to make observations
Webster's English Dictionaryob.serv.er \*b-'z*r-v*r\ n : one that observes : as : a representative sent to observe but not participate officially in a ga thering : one who accompanies the pilot of an airplane to make observations