Fruit, millions in Spanish city (5)
I believe the answer is:
lemon
'fruit' is the definition.
(I know that lemon is a type of citrus fruit)
'millions in spanish city' is the wordplay.
'millions' becomes 'm' (abbreviation for millions).
'in' indicates putting letters inside.
'spanish city' becomes 'leon' (Leon is a city in Spain).
'm' inserted into 'leon' is 'LEMON'.
(Other definitions for lemon that I've seen before include "something unattractive" , "Citrus fruit (is it the answer?)" , "Fruit - 11 (anag)" , "Defective object" , "leaving bitter taste?" .)