Synonyms for Alarming:

adj.

amazing (adjective)
awesome.
awful (adjective)
horrendous, unpleasant, frightful, horrible, ghastly, dreadful, terrible, repulsive, horrid, awful, hideous, dire, appalling.
causing fear (adjective)
disquieting, disturbing, dangerous, frightening, frightful, distressing, startling.
frightening (adjective)
terrifying, nightmarish.
threatening (adjective)
minatory.

n.

awesome, eerie, spooky. alarming (noun)
ghastly, creepy, grim, terrible, appalling, fearsome, nightmarish, baleful, hairy, atrocious, forbidding, sinister, ugly, dreadful, shivery, creepy-crawly, stupefying, gruesome, scarey, terrifying, dire, scary, bloodcurdling, horrifying, horrific, minacious, direful, awful, horrible, menacing, dreaded, dread, hair-raising, redoubtable, shuddery, petrifying, unnerving, dismaying, frightening, terrific, minatory, chilling, grisly, frightful, ominous, formidable, threatening, horrendous, fearful, macabre.

v.

alarming (verb)
shocking, startling, signaling, surprising, dismaying.
frightening (verb)
setting on edge, Scaring, harrowing, rattling, terrifying, intimidating, haunting, disturbing, horrifying, unnerving, agitating, petrifying, panicking, frightening.
warning (verb)
threatening, Advising, warning, Cautioning, alerting.

Other synonyms:

disquieting, awesome, spooky, eerie, dangerous, distressing. Other relevant words:
creepy-crawly, creepy, direful, chilling, menacing, gruesome, distressing, formidable, sinister, grisly, grim, horrific, minatory, awesome, scary, nightmarish, bloodcurdling, minacious, hair-raising, fearsome, stupefying, dangerous, spooky, disquieting, macabre, forbidding, redoubtable, horrendous, shuddery, terrific, baleful, ugly, atrocious, shivery, eerie, scarey, hairy, ominous, fearful, dreaded, dread.

Usage examples for alarming

  1. Another alarming object in marriage is that, by affinity, you become connected with the relations of the wife. – Curiosities of Literature, Vol. 1 (of 3) by Isaac D'Israeli
  2. I say that mine were extremely alarming – In a Glass Darkly, v. 3/3 by Joseph Sheridan Le Fanu
  3. I first discovered young ladies putting snuff into their mouths as if eating it, when my curiosity was excited to an alarming extent, but on being invited to 'dip' with them I soon learned that they were not eating, but 'rubbing and chewing' it, as they called it, and in such a lively manner as to soon convince me that they appreciated it. – Tobacco; Its History, Varieties, Culture, Manufacture and Commerce by E. R. Billings