Sure, it might be annoying that "literally" has come to mean "figuratively," but you'll be pretty happy that you're not facing the literal consequences of these words. Whether we're talking about spooky spirits, or staring down death, these words have lost their literal danger over time.
Clue
As with any good mystery, there are a few etymological clues here. With Germanic roots, a "clew" is a ball of thread, possibly leading to a clue that must be unraveled. In the story of the labyrinth in Greek mythology, Theseus used thread to find his way out, following the "clew" for directions.
Deadline
Thank goodness your weekly "deadlines" aren't literal. During the American Civil War, a boundary line was placed around prison camps. If any prisoners crossed it, they would discover the literal meaning of the "deadline."
Lukewarm
This one isn’t as bizarre as it is redundant. “Luke” is a common modern name, but in Middle English it meant tepid. And if someone asked for warm milk, you would heat it to a tepid temperature. Yes, that’s right — "lukewarm" means tepid tepid.
Lunatic
Derived from Latin, lunaticus means moonstruck. It refers to periodic spells of insanity tied to the appearance of the full moon. While it's likely just folklore, the phenomenon is still debated as crime tends to spike during full moons.
Mortgage
This word has its roots in Old French, but its translation is quite macabre. Mort gage translates from French to "death pledge." But in modern usage it refers to the death (end) of a financial obligation. Quite simply, a mortgage is a payment you’ll be making until completion (not until your death, as your Dad might joke).
Muscle
This bodily term is derived from the Greek word mys, which means mouse. It's not that mice are outrageously strong, but the shape and movement of some muscles were thought to resemble the whiskery little mammal.
Nightmare
Bad dreams are named after an evil spirit that visits in the night. "Mare" referred to the spooky visitor in Old English. Henry Fuseli’s painting "The Nightmare" accurately captures the superstitious definition.
Salary
Don't be so quick to turn down the saltshaker — it might be worth something! In ancient Rome, sal, or salt, was a valuable commodity, sometimes used as payment. The English word "salary" comes from the Latin salarium.