The Collaborative International Dictionary of English v.0.48:
Missioner \Mis"sion*er\, n. A missionary; an envoy; one who conducts a mission. See Mission, n., 6. "Like mighty missioner you come." --Dryden. [1913 Webster]WordNet (r) 3.0 (2006):
missioner n 1: someone sent on a mission--especially a religious or charitable mission to a foreign country [syn: missionary, missioner]