A case of one and one not making two (6)
I believe the answer is:
eleven
'two' is the definition.
The answer and definition can be both quantities as well as being singular nouns.
Maybe there's a link between them I don't understand?
'a case of one and one not' is the wordplay.
'a case of' means to remove the middle letters (outsides of).
'one' becomes 'especial' (I've seen this before).
'and' means one lot of letters go next to another.
'one not' becomes 'even' (I can't explain this - if you can you should give a lot more credence to this answer).
'especial' with its centre taken out is 'el'.
'el'+'even'='ELEVEN'
'making' is the link.
Can you help me to learn more?
(Other definitions for eleven that I've seen before include "Cricket 18" , "Cricketing side" , "Football or cricket team?" , "Football team; number" , "Time for the mid-morning tea break?" .)