sing-along

Middle English singen, from Old English singan "to chant, sing," especially in joy or merriment; "celebrate, or tell in song" (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." Also used in late Old English of birds and wolves, and sometimes in Middle English also "play on a musical instrument."

There are said to be 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 for "to sing" 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.

The sense of "utter enthusiastically" (of praises, etc.) is from 1560s. The criminal slang sense of "to confess to authorities" is attested as early as 1610s, but modern use probably is a fresh formation early 20c. To sing for one's supper, implying lack of funds, is by 1745.

Every child should be taught, from its youth, to govern its voice discreetly and dexterously, as it does its hands ; and not to be able to sing should be more disgraceful than not being able to read or write. For it is quite possible to lead a virtuous and happy life without books, or ink ; but not without wishing to sing, when we are happy ; nor without meeting with continual occasions when our song, if right, would be a kind service to others. [Ruskin, "Rock Honeycomb"]

Middle English, from Old English andlang "entire, continuous; extended" (adj.); also "alongside of" (prep.); from and- "opposite, against" (from Proto-Germanic *andi-, *anda-, from PIE *anti "against," locative singular of root *ant- "front, forehead") + lang "long" (see long (adj.)).

Reinforced by its Old Norse cognate endlang. The prepositional sense was extended in Old English to "through the whole length of." Of position, "lengthwise," from c. 1200; of movement, "onward," from c. 1300. The meaning "in company, together" is from 1580s. All along "throughout" is attested from 1690s.