Twelfth sign of the zodiac (6)
I believe the answer is:
pisces
'twelfth sign of the zodiac' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for pisces that I've seen before include "The twelfth sign of the zodiac, the fishes" , "Fish star sign" , "Spice for the Fish" , "stars" , "'Sign of the zodiac, the fish (6)'" .)