'ill-preparedness' originates from English, specifically the elements 'ill-' + 'prepare' + '-ness', where 'ill-' meant 'badly' (a negative/adverse prefix), 'prepare' came from Latin 'praeparare' meaning 'to make ready', and the suffix '-ness' formed nouns denoting a state or condition.

'prepare' entered English via Old French (preparer) from Latin 'praeparare'; the prefix 'ill-' has Old English/Old Norse roots (Old English 'yfel' / Old Norse 'illr') meaning 'bad' or 'badly'; the noun-forming suffix '-ness' comes from Old English '-nes(s)e'. These elements combined in Modern English to form 'ill-preparedness'.

Initially the elements meant 'badly' + 'to make ready' + 'state', and over time the compounded noun came to mean specifically 'the condition of not being adequately prepared' in modern usage.