These words are synonyms, each meaning "unfit to be eaten," "not eatable": "The dinner was inedible (or uneatable)." Inedible is more often used and does not carry the label of "informal" which uneatable does. Inedible applies to something that could be eaten if it were properly prepared, cooked, or ripened, whereas uneatable is more likely to be applied to items never intended to be eaten, at least not by normal people or animals: wood, coal, iron, chalk, cloth, and the like.
Dictionary of problem words and expressions. Harry Shaw. 1975.