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 (cf. 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.