Just curiosity, but does the adjective "grave" is somewhat related to the noun "grave"?
Native speaker’s answer
Rebecca
While it's difficult to say if the adjective "grave" originates from the nouns "grave" or "graveyard," it's easy to make the connection between the two as both refer to or describe things of a serious, solemn nature. Ex: The man had a grave expression on his face. Ex: The woman's grave was visited regularly by her family.