The seventh sign of the Zodiac (5)
I believe the answer is:
libra
'the seventh sign of the zodiac' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for libra that I've seen before include "Seventh sign of the Zodiac" , "Person born under Scales sign" , "Balance constellation" , "Scales star sign" , "The Scales in astrology" .)