Bang

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mid 16th century: imitative, perhaps of Scandinavian origin; compare with Old Norse bang ‘hammering’.

wiktionary

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From Middle English *bangen, from Old English *bangian, bangan or Old Norse banga(“to pound, hammer”); both from Proto-Germanic *bang-(“to beat”), from Proto-Indo-European *bʰen-(“to beat, hit, injure”). Cognate with Icelandic banga(“to pound, hammer”), Old Swedish bånga(“to hammer”), Danish banke(“to beat”), bengel(“club”), Low German bangen, bangeln(“to strike, beat”), West Frisian bingel, bongel, Dutch bengel(“bell; rascal”), German Bengel(“club”), bungen(“to throb, pulsate”).

In the sense of a fringe of hair, from bang off.

bang ( uncountable)

etymonline

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bang (v.)

1540s, "to strike hard with a loud blow," an imitative formation, or else from a Scandinavian source akin to Old Norse banga "to pound, hammer" also of echoic origin. Slang meaning "have sexual intercourse with" attested by 1937. As an adverb, "suddenly, abruptly," by 1828, probably from the notion of "with a sudden or violent sound." Related: Banged; banging. Banging (adj.) in the slang sense of "large, great, surpassing in size" is attested by 1864. Bang-up (adj.) "excellent, first-rate, in fine style" (1810) probably is shortened from a phrase such as bang up to the mark.

bang (n.)

1540s, "heavy, resounding blow;" see bang (v.). Meaning "loud, sudden explosive noise" is by 1855.

This is the way the world ends

Not with a bang but a whimper

[T.S. Eliot, from "Hollow Men," 1925]