LSJ adverb. in acc. δίκην, in the way of, after the manner of, c. gen., λύκοιοAeschylus A.Ag 1444
ἄτιμα δ’ οὐκ ἐπραξάτην.
ὁ μὲν γὰρ οὕτως, ἡ δέ τοι κύκνου δίκην
τὸν ὕστατον μέλψασα θανάσιμον γόον
κεῖται, φιλήτωρ τοῦδ’· ἐμοὶ δ’ ἐπήγαγεν
εὐνῆς παροψώνημα τῆς ἐμῆς χλιδῆς.
The pair has met no undeserved fate. For he lies thus; while she, who, like a swan, 1445has sung her last lament in death, lies here, his beloved; but to me she has brought for my bed an added relish of delight.
κύκνου δίκη: in the manner of a swan singing ...
J.P. Harris[1] says this is the earliest reference to the Swan Song which was picked up by the other Tragedians.
[1]Cassandra’s Swan Song:
Aeschylus’ Use of Fable in Agamemnon
John Philip Harris
http://www.google.com/url?sa=t&rct=j&q= ... 0087,d.dmg