One of five born together (4)
I believe the answer is:
quin
'one of five born together' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for quin that I've seen before include "One of five born together (abbr)" , "One of five in a litter" , "One of five children born at one birth" , "one of an emerging group" , "One of five born at single birth" .)