Macateer, McAteer, McAtee, or any other anglicised phonetic spelling such as McIntyre, is not based on a surname meaning 'son of a nun'.
You're right of course, pangur - I didn't notice autocorrect had "helped" my spelling.
I had meant to say Macatoor (not Macateer), sometimes spelt McAtoor, from Mac an tSiúr which does mean son of a (religious) sister, or son of a nun.
Not a common name, but I know a couple of proud bearers 