See a set, possibly as a social group (5)
I believe the answer is:
caste
'a social group' is the definition.
(I've seen this before)
'see a set possibly' is the wordplay.
'see' becomes 'c' (the word for the letter, according to Chambers**).
'possibly' is an anagram indicator.
'set' anagrammed gives 'ste'.
'c'+'a'+'ste'='CASTE'
'as' is the link.
(Other definitions for caste that I've seen before include "Social position" , "Social status" , "Persons with class" , "Hereditary class (in India)" , "place in society" .)