Idiom medium 29 / 51
“one fell swoop”
i · The common misuse One wrong form
ii · What it meansTwo lines, no filler
From Shakespeare's Macbeth: 'fell' in the older sense means fierce or deadly (same root as 'felon'). 'Foul swoop' is a mondegreen — 'fell' has drifted out of everyday use.
iii · Memory hookKeep this one
Fell = fierce (as in felon). Macbeth's hell-kite killed 'at one fell swoop' — one fierce dive.