A must is something that’s so important it can’t be missed or ignored. When you’re taking kayaking lessons, a lifejacket is a must.
Anything that is required is a must: drinking enough water is a must for being healthy. When you adopt a new dog, making sure he’ll get along with your cat is a must. Another meaning of the noun must is a stale, stuffy smell. Your damp basement and dry, hot attic might both smell of must. This meaning comes from the adjective musty, a variation on the older, now obsolete moisty.
a necessary or essential thing
highly recommended“a book that is
basic and fundamental
the quality of smelling or tasting old or stale or mouldy
grape juice before or during fermentation