Unfathomable
Part of speech: adjective
Definition: impossible to fathom or understand; incomprehensible difficult to penetrate.
Example sentence: After the separation of children from families seeking to join the United States was embraced as the official policy of our government, we should ask ourselves what story we will tell. President Trump's story is one of cruelty - that we may do something unfathomable to deter families from coming to America.
Abysmal
Part of speech: adjective
Definition: Pertaining to, or resembling an abyss; bottomless; unending; profound; fathomless; immeasurable.Extremely bad.
Example sentence: Skyjackers had a pretty abysmal success rate - once you commandeered a plane in American airspace, your odds of a happy ending were slim. After the epidemic ended in 1973, what folks tended to remember most about the skyjackers was their futility.