/ hɒˈrendəs; NAmE hɔːˈr-; hɑːˈr-/ adjective
1.
extremely shocking
SYN horrific , horrifying :
horrendous injuries
2.
extremely unpleasant and unacceptable
SYN terrible :
horrendous traffic
HELP NOTE : Some speakers do not pronounce the 'h' at the beginning of horrendous and use 'an' instead of 'a' before it. This now sounds old-fashioned.
► hor·ren·dous·ly adverb :
horrendously expensive
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WORD ORIGIN
mid 17th cent.: from Latin horrendus (gerundive of horrere (of hair) stand on end) + -ous .