godspeed (interj.) Look up godspeed at Dictionary.com
also God speed, by late 14c., "(I wish that) God (may) grant you success," from God + speed (v.) in its old sense of "prosper, grow rich, succeed." Specifically as a salutation by mid-15c. Also in Middle English as an adverb, "quickly, speedily" (early 14c.); the then-identically spelled God and good seem to be mixed up in this word. From late 13c. as a surname. He may bidde god me spede is found in a text from c.1300.