Something that's alarming is disturbing or upsetting. It can be alarming when you hear a sudden, loud crash of thunder.

The idea of climate change is very alarming to many people, and the sound of a police car's siren is alarming when you're driving. Things that are alarming grab your attention, and either frighten you or at least unsettle you. The adjective alarming comes from alarm, via the Old French alarme, which is rooted in the Italian interjection all'arme, a rally or warning cry, "to arms!"

Definitions of alarming

adj frightening because of an awareness of danger

appalling, dismaying
causing consternation
atrocious, frightful, horrible, horrifying, ugly
provoking horror
awful, dire, direful, dread, dreaded, dreadful, fearful, fearsome, frightening, horrendous, horrific, terrible
causing fear or dread or terror
baleful, forbidding, menacing, minacious, minatory, ominous, sinister, threatening
threatening or foreshadowing evil or tragic developments
bloodcurdling, hair-raising, nightmarish
extremely alarming
chilling, scarey, scary, shivery, shuddery
provoking fear terror
creepy, creepy-crawly
causing a sensation as of things crawling on your skin
formidable, redoubtable, unnerving
inspiring fear
ghastly, grim, grisly, gruesome, macabre, sick
shockingly repellent; inspiring horror
hazardous and frightening
paralyzing with terror
shocking with surprise and consternation
terrific, terrifying
causing extreme terror
not alarming; assuaging alarm

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