'nonpatient' originates from Modern English, composed of the prefix 'non-' (from Latin 'non' meaning 'not') plus 'patient', which comes from Latin 'patiens' (present participle of 'patior').

'patient' entered English via Old French/Latin (Old French 'patient', Medieval Latin 'patiens') and Middle English forms such as 'pacient'/'patient'; the negative prefix 'non-' has long been used in Modern English to form compound negatives like 'non- + noun/adjective', producing 'nonpatient'.

Originally, Latin 'patiens' meant 'suffering' or 'enduring'; in English 'patient' developed senses including 'one who receives medical care' and 'able to endure'. 'Nonpatient' simply negates the modern senses, and has come to be used chiefly to mean 'not a patient' in institutional/medical contexts.