One third of twelve — not odd number (6)
I believe the answer is:
eleven
'odd number' is the definition.
(I've seen this before)
'one third of twelve not' is the wordplay.
'one third of twelve' becomes 'e' (vrd letter of 'twelve').
'not' becomes 'leven' (I can't justify this - if you can you should give a lot more credence to this answer).
'e'+'leven'='ELEVEN'
Can you help me to learn more?
(Other definitions for eleven that I've seen before include "Number on a soccer team" , "'Legs' bingo number" , "sports team?" , "Lowest two-digit prime" , "Football side" .)