Something one could play by oneself (5)
I believe the answer is:
apart
'something' is the definition.
Both the definition and answer are adverbs.
Maybe they are linked in a way I don't understand?
'one could play by oneself' is the wordplay.
I cannot quite understand how this works, but
'one' could be 'a' (a thing is one thing) and 'a' is present in the answer.
The remaining letters 'part' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for apart that I've seen before include "away" , "First Christmas present from my love" , "Estranged - in pieces" , "In pieces; separate" , "out on a limb?" .)