what is a nuns priest?

Answer 1

You must be referring to the section of Chaucer's "Canterbury Tales" called "The Nuns' Priest's Tale".
The Nuns' priest was definitely a man and not a Mother Superior or an Abbess.
Female religious orders did not allow any males in their convents except one, an ordained priest who celebrated masses and conducted services, gave communion or extreme unction, listened to confessions, carried the Host in a reliquary at processions. Nuns were not allowed to do any of these things.
The modern term for a "Nuns' priest" would be the "Chaplain".

I went to Convent School and there was such a priest who looked after the moral welfare of the community and although he lived in the convent, had a room in a completely different area of the buildings and ate his meals with visitors and lay staff, separately from the nuns .

Answer 2

The head Nun is known as an Abbesswhich is the female superior, or Mother Superior, of an abbey of nuns.

Answer 3

This how Sister Madelene de la crux came to dominate nuns in Spain
and amaze the whole world with he miracles. People were unaware
that she had dark secret only to be revealed after 40 years!

Answer 4

http://www.gordonjacob.com/w_nun.html

http://faculty.goucher.edu/eng330/chaucernuns_priest.htm