Posted by Peter on July 25, 2003
Meanings and Origins gives for this phrase:
From Shakespeare's Macbeth.
MACDUFF: [on hearing that his family and servants have all been killed]
He has no children. All my pretty ones?
Did you say all? O hell-kite! All?
What, all my pretty chickens and their dam
At one fell swoop?
The kite referred to is a hunting bird, like the Red Kite, which was common in England in Tudor times. The 'fell swoop' (or stoop as is now said) is the rapid descent made by the bird when capturing prey."
I think it's not clear from this explanation that the word "fell" has nothing whatever to do with the kite "falling" upon its prey. My old Webster's 2nd Unabridged gives "swoop: to descend swiftly with closed wings, as a hawk [etc]"; but "fell", from Old French 'fel', means "cruel; barbarous; fierce [etc]" as in 'While we devise fell tortures for thy faults.'