'unpractical' originates from the negative prefix 'un-' (Old English/Proto-Germanic), specifically the prefix 'un-' where 'un-' meant 'not', combined with 'practical' which ultimately comes from Latin 'practicus' via Greek 'praktikos', where 'prakt-' meant 'to do'.

'practical' changed from Old French 'pratique' and Middle English forms such as 'practikal' and eventually became the modern English word 'practical'. The negative prefix 'un-' was later attached in Modern English to form 'unpractical'.

Initially 'practical' carried the sense 'fit for action or practice' (from Greek/Latin roots), and over time 'unpractical' came to mean 'not practical' or 'unsuitable for real use'.