- plus one?
I believe the answer is:
'plus one?' is the definition.
The definition and answer can be both quantities as well as being singular nouns.
Maybe they are linked in a way I don't understand?
This is the entire clue.
Can you help me to learn more?
(Other definitions for twelve that I've seen before include "disciples" , "Midday" , "Basis of duodecimal system" , "Number of centuries needed for MCC" , "Number of Apostles" .)