WordWeb Online

1. Frightening because of an awareness of danger

1. Fill with apprehension or alarm; cause to be unpleasantly surprised
   - dismay, appal [Brit, Cdn], appall [US], horrify
    
2. Warn or arouse to a sense of danger or call to a state of preparedness
   "The empty house alarmed him"
   - alert

See also: alarm, alarmingly, alarmist, appalling, atrocious, awful, baleful, bloodcurdling, chilling, consternation, creepy, creepy-crawly, dire, direful, dismay, dismaying, doubtable [archaic], dread, dreaded, dreadful, fearful, fearsome, forbidding, formidable, frightening, frightful, ghastly, grim, grisly, gruesome, hair-raising, hairy, horrendous, horrible, horrific, horrifying, macabre, menacing, minacious, minatory, nightmarish, ominous, petrifying, redoubtable, scarey [non-standard], scary, shivery, shuddery, sick, sinister, spine-chilling, stupefying, terrible, terrific [archaic], terrifying, threatening, ugly, unnerving

Type of: affright, fright, frighten, scare, warn

Antonym: unalarming

Encyclopedia: Alarm