Number often reduced (3)
I believe the answer is:
'number' is the definition.
(ten is a number)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for ten that I've seen before include "How many" , "Dudley Moore/Bo Derek film" , "honour" , "X-WORD" , "PM's address, Downing St" .)