'anti-canonical' originates from Modern English, specifically formed from the prefix 'anti-' (from Greek 'anti' where 'anti-' meant 'against') and 'canonical' (from Medieval Latin 'canonicalis', ultimately from Greek 'kanon' where 'kanon' meant 'rule').

'canonical' came into English via Medieval Latin 'canonicalis' (from Latin/Greek 'kanon'); the prefix 'anti-' (Greek) was later attached in Modern English to form 'anti-canonical', combining the senses 'against' + 'of or relating to the canon'.

Initially the parts meant 'against' + 'rule' (i.e., 'against the canon'); over time the compound came to be used both generally for things opposed to an accepted canon and technically (in mathematics) to denote the dual/opposite of the canonical object.