Unmarried sisters (4)
I believe the answer is:
nuns
'sisters' is the definition.
(I've seen this before)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for nuns that I've seen before include "Convent residents" , "Women in religious vocations" , "Religious sisters" , "women in order" , "Sisters in order" .)