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1560s, "to move or walk in a stately manner," apparently from a dialectal survival of Old English swapan "to sweep, brandish, dash," from Proto-Germanic *swaipanan, from PIE root *swei- "to swing, bend, to turn." Meaning "pounce upon with a sweeping movement" first recorded 1630s. Spelling with -oo- may have been influenced by Scottish and northern England dialectal soop "to sweep," from Old Norse sopa "to sweep." Related: Swooped; swooping.
1540s, from swoop (v.). Phrase one fell swoop is from Shakespeare.
Oh, Hell-Kite! All? What, All my pretty Chickens, and their Damme, At one fell swoope? ["Macbeth," IV.iii.219]