'antitypal' is formed from the prefix 'anti-' (from Greek 'anti-' meaning 'against, opposite') plus 'typal' (from 'type' meaning 'model, pattern').

'typal' derives from Latin/Greek roots for 'type' (Greek 'typos'), and the modern English adjective 'typal' developed from that. The combining of 'anti-' with 'typal' produced the modern formation 'antitypal' in English to mean 'against the typical form'.

Initially the elements meant 'against' and 'type' separately; combined in modern usage they convey the idea 'against the usual type' or 'not conforming to type', a meaning that is a straightforward compositional development.