If something's execrable it's really and truly, unbelievably, absolutely the worst.
Execrable is often used as a harshly critical term in the arts, when a reviewer really wants to throw the book at something. Not surprisingly, the word comes from a Latin word meaning "to utter a curse; to hate or abhor." Tough words for bad art. Perhaps part of the power and nastiness of execrable lies in the word's similarity to excrement — but that's a vocabulary word we're not touching in this entry!