The word horrendous describes something that is extremely unpleasant, terrible or horrifying. There are several synonyms for this term that can be used interchangeably to describe similar situations or experiences. Examples of such words include appalling, gruesome, atrocious, dreadful, and ghastly. Other possible synonyms include shocking, frightful, disturbing, alarming, and hideous. Each of these words carries with it a sense of dread or some form of negativity in the form of emotional, physical, or mental distress. As such, describing something as horrendous implies that it is a highly unpleasant or undesirable experience that should be avoided at all costs.