nun

The word 'nun' entered English from Old English 'nonne', which was borrowed from Late Latin 'nonna', a title for a spiritual mother or elderly woman. This Latin term is likely a nursery word, akin to 'nana', used by children for a female caregiver. The ultimate origin is probably imitative of infantile speech, similar to other parental terms like 'mama' and 'papa'. Over centuries, this simple, familial term became specialized within Christian monasticism to denote a woman belonging to a religious order.

The word is a simplex. It is a loanword from Latin, where 'nonna' was a title of respect for an elderly woman, later a child's word for 'mother', and specifically a term for a spiritual mother or nun.