Sign of the Zodiac, the crab
I believe the answer is:
cancer
I believe this is a double definition.
'sign of the zodiac' is the first definition.
(Cancer is an example)
'the crab' is the second definition.
(I've seen this before)
(Other definitions for cancer that I've seen before include "A Tropic or a malignant disease" , "Sign of the Crab, or a Tropic" , "Fourth sign of the zodiac" , "Malignant growth and sign of the zodiac" , "Zodiac sign - tumour" .)