Content with quantity (3)
I believe the answer is:
ten
'quantity' is the definition.
(ten is a kind of quantity)
'content with' is the wordplay.
'with' indicates a hidden word.
'TEN' is hidden within 'content'.
(Other definitions for ten that I've seen before include "Roman numeral X" , "How many" , "Dudley Moore/Bo Derek film" , "Very young" , "honour" .)