1
general::
Phrase(s): in one fell swoop
Go to at one fell swoop.
McGrawhill's American Idioms And Phrasal Verbs
2
general::
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.", see ONE FELL SWOOP.
American Heritage Idioms