Plato, Laws 700b

ἑαυτῆς ἄττα καὶ σχήματα, καί τι ἦν εἶδος ᾠδῆς εὐχαὶ πρὸς θεούς, ὄνομα δὲ ὕμνοι ἐπεκαλοῦντο· καὶ τούτῳ δὴ τὸ ἐναντίον ἦν ᾠδῆς ἕτερον εἶδος—θρήνους δέ τις ἂν αὐτοὺς μάλιστα ἐκάλεσεν—καὶ παίωνες ἕτερον, καὶ ἄλλο, Διονύσου γένεσις οἶμαι, διθύραμβος λεγόμενος. νόμους τε αὐτὸ τοῦτο τοὔνομα ἐκάλουν, ᾠδὴν ὥς τινα ἑτέραν· ἐπέλεγον δὲ κιθαρῳδικούς. τούτων δὴ διατεταγμένων καὶ ἄλλων τινῶν, οὐκ ἐξῆν ἄλλο

one class of song was that of prayers to the gods, which bore the name of hymns; contrasted with this was another class, best called dirges; paeans formed another; and yet another was the dithyramb, named, I fancy, after Dionysus. Nomes also were so called as being a distinct class of song; and these were further described as citharoedic nomes. So these and other kinds being classified and fixed, it was forbidden to set one kind of words to a different class of tune.