"Fell swoop" was coined by Shakespeare
in Macbeth. "Fell" means evil, and is related to "felon." "Swoop" is related
to "sweep," which was originally its past tense.
"Hue and cry" is one of those redundant
expressions like "last will and testament" or "give and bequeath." Usually
the redundant expressions are mixed English and Latin (or law French),
but "hue and cry" is unusual in that both elements are Old French. Under
the medieval English and French custom of Hue and Cry, the witnesses of
a crime or crime scene were obliged to chase and halloo after any escaping
felon on pain of being liable for any damages he perpetrated.
"Nightmare" is from "night" and
a Germanic root meaning "demon" or "goblin," from an IE root *mer-
meaning fade away, and possibly being the same, or related to, the root
meaning kill or die which gives us murder, mortal, and many related words.
"Nightmare" meant the monster, rather than the bad dream, until possibly
the 19th century. "Mare" in the monster sense was known in English
as late as the early 18th century.
All IE languages share the word "night" from the same IE root, while "day" varies greatly from language to language. From this, it is argued that the original Indo-Europeans measured time by night, and that vestiges of this are in the English words "fortnight" and the archaic "sennight" for week (seven nights).