A sisterly surname (5)
I believe the answer is:
nolan
'surname' is the definition.
I don't know anything about this answer so I can't tell whether this works.
'a sisterly' is the wordplay.
I cannot really see how this works, but
'a' could be 'an' and 'an' is found within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for nolan that I've seen before include "Film director - singing sisters" , "Sir Sidney - - , Australian painter" .)