The expression “one fell swoop” was introduced by Shakespeare in Macbeth.
When Macduff learns that his wife and children have been murdered he exclaims:
“What, all my pretty chickens and their dam / At one fell swoop?”
Metaphorically, Macduff compares his wife and children to chickens and their murderer to a bird of prey.
During Shakespeare’s time, fell meant “fierce,” and survives today in the word felon.