The definition of horrendous is something really bad, horrible or awful.
An extremely bad and unpleasant experience is an example of a horrendous experience.
Origin of horrendousClassical Latin horrendus ; from present participle of horrere: see horrid
Hideous; dreadful: “Horrendous explosions shook the whole city” (Howard Kaplan).
Origin of horrendousFrom Latin horrendus, from gerundive of horrēre, to tremble.
From Latin horrendus, future participle of horrēre (“to dread”).