verb “must”
 must (only has one form)
- to be obligated or required to do something Sign up to see the translation of definitions and examples into any language. 
 You must wear a helmet to ride the bike safely. 
- to indicate a high likelihood or certainty of something being true She must know the answer, she studied all night. 
noun “must”
 singular must, plural musts
- an essential or necessary thing For a successful cake, precise measurements are a must.