This etymology is probably older than Plato. With the basic three components σέλας, νέος and ἀεί, it is repeated during all Antiquity as the standard etymology. Plato adds in fact a fourth component, ἔνος "old", which is not found in other sources. The words is parsed as a compound uniting a noun, one or two adjectives ("new" in the standard version, and in Platon "new" and "old") and an adverb ("always"). More importantly, the etymology starts not from the standard form of the word "moon" in Ionic-Attic, σελἠνη, but from a derived poetic form σελαναία, which is in fact Doric. Starting from a dialectal variant whenever it was more convenient was not uncommon in Greek etymology, and there are other examples in the Cratylus. Notice that this etymology assumes as the last ‘primary element’ the adverb ἀεί under its Attic form, not paying attention to the fact that the older form is αἰεί (Homeric and Ionic) and that Doric dialects have αἰές with the same diphthong [ai]. A variant of the etymology, found in Byzantine Etymologica (see Parallels), implies only two components, σέλας and νέον, and drops "always"