Old English singan "to chant, sing, celebrate, or tell in song," also used of birds (class III strong verb; past tense sang, past participle sungen), from Proto-Germanic *sengwan (source also of Old Saxon singan, Old Frisian sionga, Middle Dutch singhen, Dutch zingen, Old High German singan, German singen, Gothic siggwan, Old Norse syngva, Swedish sjunga), from PIE root *sengwh- "to sing, make an incantation." The criminal slang sense of "to confess to authorities" is attested from 1610s.
No related forms in other languages, unless perhaps it is connected to Greek omphe "voice" (especially of a god), "oracle;" and Welsh dehongli "explain, interpret." The typical Indo-European root is represented by Latin canere (see chant (v.)). Other words meaning "sing" derive from roots meaning "cry, shout," but Irish gaibim is literally "take, seize," with sense evolution via "take up" a song or melody.
Old English sang "voice, song, art of singing; metrical composition adapted for singing, psalm, poem," from Proto-Germanic *songwho- (source also of 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.