in one fell swoop

All at once, with a single decisive or powerful action. When the economy crashed, thousands lost their jobs, their homes, and their pensions in one fell swoop. As the two leaders ratified the treaty, 10 years of civil war ended in one fell swoop. In her explosive new novel, the acclaimed author seeks to tackle issues of race, gender, and religion in one fell swoop.

one fell swoop, in

Also at one fell swoop. All at once, in a single action, as in This law has lifted all the controls on cable TV in one fell swoop. This term was used and probably invented by Shakespeare in Macbeth (4:3), where the playwright likens the murder of Macduff's wife and children to a hawk swooping down on defenseless prey. Although fell here means "cruel" or "ruthless," this meaning has been lost in the current idiom, where it now signifies "sudden."

in (or at) one fell swoop

all in one go.

This expression comes from Macduff's appalled reaction to the murder of his wife and children in Shakespeare's Macbeth: ‘Oh hell-kite!…All my pretty chickens, and their dam At one fell swoop?’

at/in one fell ˈswoop

with a single action or movement; all at the same time: Only a foolish politician would promise to lower the rate of inflation and reduce unemployment at one fell swoop.