"giving forth a loud sound like a trumpet," mid-15c., present-participle adjective from blare. Of qualities other than sound, by 1866.
Entries linking to blaring
blare v.
late 14c., bleren "to wail," possibly from an unrecorded Old English *blæren, or from Middle Dutch bleren "to bleat, cry, bawl, shout." Either way probably echoic. Related: Blared; blaring. As a noun from 1809, from the verb.