Spanish aunt on river with a headdress (5)
I believe the answer is:
tiara
'headdress' is the definition.
(tiara is a kind of headdress)
'spanish aunt on river with a' is the wordplay.
'spanish aunt' becomes 'tia' ('aunt' in Spanish).
'on' is a charade indicator (letters next to each other).
'river' becomes 'r' (abbreviation for river).
'with' says to put letters next to each other.
'tia'+'r'+'a'='TIARA'
(Other definitions for tiara that I've seen before include "special headgear" , "Jewelled hair-band" , "Type of diadem" , "It might go to one's head" , "it goes to one's head!" .)