How do you spell Poseidon in ancient Greek? Spelling in Attic is: Ποσειδῶν (with contraction). Answered 2015-09-23 · Upvoted by Chad Turner, Classics PhD, specializing in Greek tragedy and Greek/Roman mythology [Originally posted on http://quora.com/How-do-you-spell-Poseidon-in-ancient-Greek/answer/Nick-Nicholas-5]