the.com/bromide

A soothing cliché prescribed like a sedative, because it once literally was one.

means A trite, worn-out saying trotted out to soothe or placate, especially one so predictable it numbs rather than comforts.

from From bromine, the element — in the 1800s, potassium bromide salts were widely prescribed as sedatives for anxiety, insomnia, and even epilepsy. By the early 1900s, 'bromide' had drifted from the medicine cabinet into language itself: a dull, calming platitude that dulls the mind the way the drug dulled the nerves. The writer Gelett Burgess helped cement the figurative sense in a popular 1906 book that cast 'bromides' as walking clichés — people whose every remark was a tranquilizing commonplace.

origin
Potassium bromide was a 19th-century sedative drug
metaphor shift
Dull platitude sense arrived by early 1900s
chemistry
Technically any compound of bromine plus another element
irony
The drug calmed nerves, the phrase just numbs conversation
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