If I undersand the question correctly, a few synonyms for must or must have would be require, prerequisite, requisite well yes... but you could also say needed to have
"Need" or "have to."
'There must be' could be one.
have to
unmissable
You must have two words for a pair of synonyms. You cannot have a single word that is a synonym, because synonym means two (or more) words that mean the same thing.
Synonym: leftovers so the opposite must be whole.
What is synonym for merchant? What is synonym for merchant?
synonymize
What is the synonym government.
you are a synonym of abandoned.
a synonym to..?
no it is not a synonym