HORRENDOUS
awful, dire, direful, dread, dreaded, dreadful, fearful, fearsome, frightening, horrendous, horrific, terrible
(adjective) causing fear or dread or terror; “the awful war”; “an awful risk”; “dire news”; “a career or vengeance so direful that London was shocked”; “the dread presence of the headmaster”; “polio is no longer the dreaded disease it once was”; “a dreadful storm”; “a fearful howling”; “horrendous explosions shook the city”; “a terrible curse”
Source: WordNet® 3.1
Etymology
Adjective
horrendous (comparative more horrendous, superlative most horrendous)
Extremely bad; awful; terrible.
Synonyms
• awful, horrific, terrible, dreadful
Trivia
One of four common words ending in -dous, which are hazardous, horrendous, stupendous, and tremendous.
Source: Wiktionary
Hor*ren"dous, a. Etym: [L. horrendus.]
Definition: Fearful; frightful. [Obs.] I. Watts.
Source: Webster’s Unabridged Dictionary 1913 Edition