Synonyms/Hypernyms (Ordered by Estimated Frequency) of noun must

3 senses of must

Sense 1
must -- (a necessary or essential thing; "seat belts are an absolute must")
       => necessity, essential, requirement, requisite, necessary -- (anything indispensable; "food and shelter are necessities of life"; "the essentials of the good life"; "allow farmers to buy their requirements under favorable conditions"; "a place where the requisites of water fuel and fodder can be obtained")

Sense 2
must -- (grape juice before or during fermentation)
       => grape juice -- (the juice of grapes)

Sense 3
mustiness, must, moldiness -- (the quality of smelling or tasting old or stale or mouldy)
       => staleness -- (having lost purity and freshness as a consequence of aging)

Antonyms of adj must

1 sense of must

Sense 1
must (prenominal) -- (highly recommended; "a book that is must reading")

INDIRECT (VIA essential) -> inessential, unessential -- (not basic or fundamental)

Similarity of adj must

1 sense of must

Sense 1
must (prenominal) -- (highly recommended; "a book that is must reading")
       => essential (vs. inessential) -- (basic and fundamental; "the essential feature")