Necessity (12)
There are a few possibilities for this:
prerequisite
'necessity' is the definition.
(I know that need is a type of necessity)
This is the entire clue.
(Other definitions for need that I've seen before include "A condition" , "Require (as essential)" , "Exigency" , "Lack - demand" , "'miss'" .)
'necessity' is the definition.
(I know that must is a type of necessity)
This is the entire clue.
(Other definitions for must that I've seen before include "The mould is compelled" , "Prerequisite" , "Unfermented wine" , "Smell of dampness or staleness" , "Is obliged to" .)
'necessity' is the definition.
(thesaurus)
This is the entire clue.
(Other definitions for prerequisite that I've seen before include "Needed as a prior condition" , "Something required as a prior condition" , "Early qualification" .)