'atypicality' originates from modern English, specifically formed from the adjective 'atypical' + the noun-forming suffix '-ity', where the prefix 'a-' (from Greek) meant 'not' and 'typical' derived from Greek 'tupos' via Latin/French meaning 'model' or 'impression'.

'atypical' was formed in English by adding the negative prefix 'a-' to 'typical' (itself from Latin/French roots), and later the suffix '-ity' was attached to create the noun 'atypicality' in modern English.

Initially it simply conveyed 'not typical' (the negative of 'typical'); over time it came to mean more specifically 'the condition or degree of deviating from the norm', including technical uses in medicine and statistics.