One man's universe (6)
I believe the answer is:
cosmos
'one man's universe' is the definition.
'cosmos' can be an answer for 'universe' (synonyms). I am unsure of the 'one man's' bit.
'man's universe' is the wordplay.
'man' becomes 'Cos'.
'universe' becomes 'mos' (I can't justify this - if you can you should give a lot more credence to this answer).
'cos'+'mos'='COSMOS'
Can you help me to learn more?
(Other definitions for cosmos that I've seen before include "Universe as an ordered system" , "The entire universe." , "Everything that exists" , "Universe seen as a whole" , "The universe, whole of creation" .)