Adulthood (8)
(Other definitions for majority that I've seen before include "Greater number or part" , "More than half the number" , "Full age" , "The largest group" .)
'adulthood' is the definition.
(I know that adulthood can be written as maturity)
This is the entire clue.
(Other definitions for maturity that I've seen before include "State of full growth or adulthood" , "Ripeness" , "Full-grown state" , "State of having reached full development" , "Fool" .)