A diminutive relative (3)
I believe the answer is:
sis
This could be a double definition.
'a diminutive' is the first definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
'relative' is the second definition.
(short for sister)
Can you help me to learn more?
(Other definitions for sis that I've seen before include "Secret Intelligence Service (abbr.)" , "relative" , "Secret Intelligence Service (abbreviation)" , "Family member (informal)" , "Relative's" .)