To make or become musty.
To be compelled.
To be necessary.
Mustiness; mold.
The expressed unfermented juice of the grape.
Oh, I believe it must be that! – Marie Bashkirtseff (From Childhood to Girlhood) by Marie Bashkirtseff
" It must be Mr. Percival. – Salome by Emma Marshall
Must I tell you that? – The Shrieking Pit by Arthur J. Rees