'undisclosable' originates from Modern English, specifically formed from the prefix 'un-' + the verb 'disclose' + the adjectival suffix '-able', where 'un-' meant 'not', 'dis-' meant 'apart' (from Latin roots), and 'close' (from Latin 'claudere') meant 'to shut'.

'disclose' came into English via Old French 'desclore' (later 'desclore'/'desclore') from Latin components 'dis-' + 'claudere' (to shut). From this verb the adjective-forming suffix '-able' produced 'disclosable'/'disclosible' in English, and adding the negative prefix 'un-' produced 'undisclosable'.

Initially the root 'disclose' meant roughly 'to un-shut or open (make known)', and over time compounds like 'undisclosable' evolved to mean 'not able to be made known' (the negative quality of being unable to be revealed).