'nonpublic' originates from English, built from the prefix 'non-' (ultimately from Latin 'non') meaning 'not', and 'public' (from Latin 'publicus'), where 'publicus' meant 'of the people'.

'public' changed from Latin 'publicus' to Old French 'publique' to Middle English 'publik' and eventually became modern English 'public'. The compound 'non-public' was formed in Modern English (often hyphenated) and later appears written as the solid form 'nonpublic'.

Initially it literally meant 'not public' (the negation of 'public'), and over time it has retained that basic meaning: 'not open to or intended for the public'.