Middle English bak, from Old English bæc, from Proto-Germanic *baką, possibly from Proto-Indo-European *bʰogo (literally “bending”). The adverb represents an aphetic form of aback. Compare Middle Low German bak (“back”), from Old Saxon bak, and West Frisian bekling (“chair back”), Old High German bah, Swedish and Norwegian bak. Cognate with German Bache (“sow [adult female hog]”).
Borrowed from English back.
From English back