'unannounceable' originates from English prefix 'un-' (Old English) attached to 'announceable', which ultimately derives from Latin 'annuntiare', where 'ad-' meant 'to/toward' and 'nuntiare' meant 'to report or bring news'.

'unannounceable' developed by prefixing 'un-' to the adjective 'announceable'. 'Announce' came into English via Old French (anoncier/anoncer) from Latin 'annuntiare'; Middle English forms produced modern 'announce', then 'announceable', and finally the negative form 'unannounceable'.

Initially, Latin 'annuntiare' meant 'to bring tidings' or 'to report'; over time the sense shifted to 'make known publicly' in English, and 'unannounceable' came to mean 'not suitable or not possible to be made public'.