Mom's sister (4)
'mom's sister' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for aunt that I've seen before include "Parent's female sibling" , "Put up with" , "Close relative" , "Female relation" , "Wife of one's uncle" .)
(Other definitions for auntie that I've seen before include "Relation; the BBC" , "Family relative" , "Unite a strange family member" , "Female relation" , "BBC nickname" .)