The direct translations for 魔神/Majin would be Demonic Spirit, Demonic Being, Demonic Deity, and/or Deminic God. A devil is a creature that rules over Demons. A Majin is basically a powerful Demon that causes horrible calamities or Gods who cause terrible misfortunes, but they aren't Demon Rulers.
Thanks for the info. I always thought that a majin is sort of like a powerful force or entity that has the capacity for good or evil as Dr. Kabuto suggested in the OVA Mazinkaiser.
My mistake. I guess I missed the "dai" kanji which either means "large, big, or great" in Japanese. So yeah, "Dai Majin" would translate as Great Devil God.
Great Mazinger is awsome, i will bet he can destroy any kind of robot mechainal enemy what he want to beat them. Plus he's great and Grendizer is really awsome too both super robot awsomeness.
大魔神 (Majin) Great Devil God.