Eighth sign of the zodiac (7)

I believe the answer is:

scorpio

'eighth sign of the zodiac' is the definition.
(I've seen this before)

This is the entire clue.

(Other definitions for scorpio that I've seen before include "7 [SIGN OF THE ZODIAC]" , "Zodiacal sign" , "A heavenly body" , "Astrological sign" , "star group" .)

I've seen this clue in the Sydney Morning Herald and The Mirror.

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