Dave,

“Zeus” in Ancient Greek means Zeus, i.e., the god himself. It is not related, so far as I know to Roman “deus," the Latin for (generic) god. Perhaps you are confused by the fact that the genitive form of Zeus is sometimes “Dios,” and other cases (except, interestingly, the vocative), may also begin with delta rather than Z. Autenrieth’s Homeric Dictionary says “the original meaning of the root of the word is the brightness of the sky, afterwards personified; cf. dios, Lat. sub divo.”

The generic word for god in ancient Greek is theos (theta, epsilon, omicron, sigma). See Liddell & Scott. Greek LexiconI “God, the Deity, in general sense, both sg. and pl.”

Lee