Parent's sister (6)
(Other definitions for auntie that I've seen before include "The BBC (coll.)" , "Unite a strange family member" , "Female relation" , "The Beeb" , "Untie a relative" .)
'parent's sister' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for aunt that I've seen before include "Charley's ___ , farce staged in London in 1892, revived and adapted ever since" , "Put up with" , "Female relation" , "Blood relative" , "Charley's in play?" .)