Abysm - abyss - abysmal - abyssal
There are two related nouns, with associated adjectives: abyss (abyssal) and abysm (abysmal). Both derive from the same source, Greek ἄβυσσος (abussos), which means 'bottomless, unfathomed' as an adjective and 'the deep', 'the lower levels of the ocean' as a noun - ἄβυσσος is formed from ἀ (a, emphatic) and βυσσός (bussos, a variant of βυθός (buthos, the depth (of the sea)). Abysm came via Latin, where the Greek was borrowed as late popular Latin abyssus, with the superlative abyssimus, 'the profoundest depth'. In present-day English, the two nouns are distinct.
- Abyss is the more literal word. It means the depths of the ocean. (There is a Science Fiction story by H.G.Wells of 1896 about descents in a bathysphere called 'In the Abyss'); in the Abrahamic faiths, 'the abyss' is also used to mean 'the bottomless pit' of Hell. The English adjective meaning 'to do with the depths' is abyssal.
- The other noun, abysm, is less used nowadays. It is more old-fashioned, 'poetic' and affected. The adjective abysmal is current, used in the figurative sense of 'very bad', 'the lowest of the low'. A school-teacher may, for example, describe the written work of a pupil as abysmal. The teacher is not being polite.