'inexplicableness' originates from Latin, specifically the word 'explicare', where the prefix 'ex-' meant 'out' and the root 'plicare' meant 'to fold'; the negative prefix 'in-' meant 'not', and the suffix '-able' meant 'able to be', with English nominalizing suffix '-ness'.

'inexplicableness' developed from Late Latin/Medieval Latin forms such as 'inexplicabilis' and from Old French/Anglo-Norman influences on 'inexplicable'; the adjective entered Middle English as 'inexplicable', and the noun was later formed in English by adding '-ness'.

Initially, components conveyed 'not able to be unfolded or explained'; over time the compound came to mean broadly 'not able to be explained or accounted for' in modern usage.