Horrendous

google

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mid 17th century: from Latin horrendus (gerundive of horrere ‘(of hair) stand on end’) + -ous.

wiktionary

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Borrowed from Latin horrendus, future participle of horreō(“I dread”), +‎ -ous.

etymonline

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horrendous (adj.)

1650s, from Latin horrendus "dreadful, fearful, terrible," literally "to be shuddered at," gerundive of horrere "to bristle with fear, shudder" (see horror). Earlier form in English was horrend (mid-15c.).