'antimethodical' originates from Greek and from English compounding, specifically the prefix 'anti-' from Greek 'antí' where 'antí' meant 'against', and the root 'method' from Greek 'methodos' where 'methodos' meant 'pursuit, investigation', combined with the adjectival suffix '-ical' (from Latin/Greek formation).

'methodos' (Greek) became Latin 'methodus', then Old French/Medieval Latin forms led to Middle English 'method'. From 'method' the adjective 'methodical' was formed (English, 17th century), and in modern English the prefix 'anti-' was attached to create the compound 'antimethodical' as a descriptive adjective.

Initially the components literally meant 'against method', and over time the compound has come to be used to describe behavior or approaches that are unsystematic, deliberately opposed to systematic procedure, or lacking method; the core idea remains 'against systematic method' but is applied descriptively.