Fool old lady (4)
I believe the answer is:
nana
I believe this is a double definition.
'fool' is the first definition.
(I've seen this before)
'old lady' is the second definition.
(Other definitions for nana that I've seen before include "Zola's heroine" , "Old woman" , "Darling dog" , "Relative" , "Informal grandmother" .)