| FOWL SWOOP |
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FELL SWOOP |
Poor Macduff, learning that Macbeth has had his wife and children murdered, cries “What, all my pretty chickens and their dam/At one fell swoop?” Thus enters the language a popular phrase meaning “terrible blow” (the image is of a ruthless hawk swooping down to slaughter helpless chicks).
The old meaning of “fell” to mean “savage,” “cruel,” or “ruthless” has otherwise pretty much died out, so that many people mistakenly substitute “foul” or “fowl” for “fell.” “Fell” in this sense is related to words like “felon” and “felony.”
The mangled form “swell foop” is a popular bit of humor which should at least remind you that the first word in the phrase has to rhyme with “swell.”