I suppose you're trying to give parts of speech to the MosCow categories: Must have, Should have, Could have, Would have.
As adjectives, the closest I can think of are:
'a must-have' - Necessaryadj: necessary/obligatory/requisite, n: necessity/obligation/requisite
'a should-have' - recommended adj: recommended, n:recommendation
'a could-have' or 'a nice-to-have' - possibleadj:possible/desirable, n:possibility/desire
' a'a would-have' - allowableadj:allowable/disposable./unnecessary n:??
And you can make nouns more easily out of these as you please.
The modals don't correspond as cognates to any nouns or adjectives.