'unmethodical' originates from the prefix 'un-' meaning 'not' and the word 'methodical', which comes from the Greek word 'methodikos', where 'methodos' meant 'pursuit of knowledge'.

'methodikos' transformed into the Latin word 'methodicus', and eventually became the modern English word 'methodical'. The prefix 'un-' was added to form 'unmethodical'.

Initially, 'methodical' meant 'pursuit of knowledge', but over time it evolved into its current meaning of 'systematic'. 'Unmethodical' thus means 'not systematic'.