Man is lacking in comparison - poor sign! (7)
I believe the answer is:
scorpio
'sign' is the definition.
(Scorpio is an example)
'man is lacking in comparison poor' is the wordplay.
'is lacking in' suggests deleting specific letters.
'poor' indicates anagramming the letters.
'comparison' with 'man' removed is 'copriso'.
'copriso' with letters rearranged gives 'SCORPIO'.
(Other definitions for scorpio that I've seen before include "house" , "Astrological sign" , "Sign of autumn" , "Group of stars" , "7 [SIGN OF THE ZODIAC]" .)