Points out the pin in the back (5)
I believe the answer is:
spine
'the back' is the definition.
(synonyms)
'points out the pin' is the wordplay.
'points' becomes 'se' ().
'out' means one lot of letters goes inside another.
'se' going around 'pin' is 'SPINE'.
'in' acts as a link.
(Other definitions for spine that I've seen before include "Line of vertebrae" , "Vertebral column" , "Backbone" , "Thorn" , "Strength of character" .)