He possesses special ring (5)
I believe the answer is:
mason
'he possesses special ring' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'he possesses special ring' is the wordplay.
'he' becomes 'man' ().
'possesses' indicates putting letters inside.
'special' becomes 'S' (common abbreviation as in Special Air Service).
'ring' becomes 'o'.
's'+'o'='so'
'man' enclosing 'so' is 'MASON'.
Can you help me to learn more?
(Other definitions for mason that I've seen before include "one in construction" , "Jewish comedian" , "secretive lodger!" , "One in lodge" , "One works with stone or brick" .)