'unannouncable' originates from English, built from the negative prefix 'un-' (from Old English 'un-') and the verb 'announce' (from Latin 'annuntiare'), where 'un-' meant 'not' and 'annuntiare' meant 'to report or bring news.'

'announce' came into English via Old French 'anoncer' (from Latin 'annuntiare'), developing in Middle English as forms like 'annoncen'/'anuncien'; the adjective form 'announceable' (able to be announced) later arose with the suffix '-able', and the negative prefix 'un-' was added to yield 'unannouncable' (or variant spelling 'unannounceable').

Initially the root 'annuntiare' meant 'to report or bring news'; over time the verb 'announce' came to mean 'make known', the adjective-forming '-able' gave 'announceable' ('able to be announced'), and 'un-' reversed that to mean 'not able to be announced', the current sense of 'unannouncable'.