'aposiopestic' originates from Greek, specifically from the noun 'aposiopesis' (ἀποσιώπησις), where the prefix 'apo-' meant 'away, off' and the root 'siōp-' (from 'siōpaō') related to 'silence' or 'be silent'.

'aposiopesis' entered English via Latin and Medieval/Modern usage as the noun for a sudden silence or breaking off in speech; the adjective 'aposiopestic' was formed in Modern English by adding the adjectival suffix '-ic' to denote 'relating to aposiopesis'.

Initially it referred specifically to the act or instance of abruptly stopping speech ('a sudden silence' or 'broken-off utterance'); over time the derived adjective came to mean 'relating to or characteristic of such abrupt halting in speech'.