No room possibly to accommodate unknowns found missing, maybe? (8)
I believe the answer is:
oxymoron
'missing maybe?' is the definition.
I can't tell whether this definition defines the answer.
'no room possibly to accommodate unknowns' is the wordplay.
'possibly' indicates anagramming the letters.
'to accommodate' indicates putting letters inside.
'unknowns' becomes 'xy' (I can't explain this - if you can you should give a lot more credence to this answer).
'no'+'room'='noroom'
'noroom' anagrammed gives 'omoron'.
'omoron' placed around 'xy' is 'OXYMORON'.
'found' acts as a link.
Can you help me to learn more?
(Other definitions for oxymoron that I've seen before include "Figure of speech, eg bitter sweet" , "Figure of speech using contradictory terms" , "Awfully good, for example" , "Apparently contradictory figure of speech" , "Figure of speech joining contradictory terms" .)