abyssal

Abyssal is a relatively infrequently used word, though it's derived from the more prevalent noun, "abyss." In contrast, the adjective "abysmal" is more common than its corresponding noun "abysm." All four terms descend from the Late Latin word abyssus, which is in turn derived from the Greek abyssos ("bottomless"). "Abyss" and "abysm" are synonymous (both can refer to the mythical bottomless pit in old accounts of the universe or can be used more broadly in reference to any immeasurably deep gulf), but the adjectives "abyssal" and "abysmal" are not used identically. "Abyssal" can mean "incomprehensible," but it's most often found in contexts referring to the bottom of the sea. "Abysmal" shares the oceanographic sense with "abyssal," but it more frequently means "immeasurably deep" or "absolutely wretched."