swan (n.)
Old English swan "swan," from Proto-Germanic *swanaz "singer" (cognates: Old Saxon swan, Old Norse svanr, Danish svane, Swedish svan, Middle Dutch swane, Dutch zwaan, Old High German swan, German Schwan), probably literally "the singing bird," from PIE root *swen- "to sing, make sound" (see sound (n.1)); thus related to Old English geswin "melody, song" and swinsian "to make melody."

In classical mythology, sacred to Apollo and to Venus. The singing of swans before death was alluded to by Chaucer (late 14c.), but swan-song (1831) is a translation of German Schwanengesang. The ancient Indo-European mythical swan-maiden so called by mythographers from 1829. Swan dive is recorded from 1898. A black swan was proverbial for "something extremely rare or non-existent" (late 14c.), after Juvenal ["Sat." vi. 164], but later they turned up in Australia (Chenopsis atratus).
"Do you say no worthy wife is to be found among all these crowds?" Well, let her be handsome, charming, rich and fertile; let her have ancient ancestors ranged about her halls; let her be more chaste than all the dishevelled Sabine maidens who stopped the war--a prodigy as rare upon the earth as a black swan! yet who could endure a wife that possessed all perfections? I would rather have a Venusian wench for my wife than you, O Cornelia, mother of the Gracchi, if, with all your virtues, you bring me a haughty brow, and reckon up Triumphs as part of your marriage portion. [Juvenal]