an elaborate vocal signal produced by an animal, as the distinctive sounds produced by certain birds, frogs, etc., in a courtship or territorial display.
Old English sang "voice, song, art of singing; metrical composition adapted for singing, psalm, poem," from Proto-Germanic *sangwaz (cf. Old Norse söngr, Norwegian song, Swedish sång, Old Saxon, Danish, Old Frisian, Old High German, German sang, Middle Dutch sanc, Dutch zang, Gothic saggws), from PIE *songwh-o- "singing, song," from *sengwh- "to sing, make an incantation" (see sing (v.)).
Phrase for a song "for a trifle, for little or nothing" is from "All's Well" III.ii.9 (the identical image, por du son, is in Old French. With a song in (one's) heart "feeling joy" is first attested 1930 in Lorenz Hart's lyric. Song and dance as a form of vaudeville act is attested from 1872; figurative sense of "rigmarole" is from 1895.
Very cheaply, for little money, especially for less than something is worth. For example, “I know a man ... sold a goodly manor for a song” (Shakespeare, All's Well That Ends Well, 3:2). This idiom alludes to the pennies given to street singers or to the small cost of sheet music. [Late 1500s]
