1 extremely shocking; terrible:
horrendous injuries * The police officer said the attack was the most horrendous he had ever seen.
2 extremely unpleasant and unacceptable:
horrendous traffic * They have horrendous financial problems.
HELPNOTE Some people use an instead of a before this word and then usually do not pronounce the 'h'. This now sounds old-fashioned.
horrendously adverb:
horrendously expensive
