'antimethodic' originates from the prefix 'anti-' (from Greek 'anti' meaning 'against') combined with 'methodic' (from Late Latin 'methodicus', via Greek 'methodos').

'antimethodic' was formed by prefixing 'anti-' to English 'methodic' (which came via Late Latin 'methodicus' from Greek 'methodos'), yielding the compound meaning 'against or not following method'.

Initially it literally meant 'against method' (i.e., opposed to a particular method); over time its use has settled to the broader descriptive sense 'not methodical' or 'unsystematic'.