How do you use the word grief in a verb form and adverb form?

Answer 1

The verb for grief is grieve.
Other verbs are grieves, grieving and grieved, depending on the tense you are writing or speaking in.

Some example sentences are:
"We all grieve the loss".
"He grieves for humanity".
"We are all grieving".
"We grieved the death of Goldy the Goldfish for weeks".

Answer 2

Grief is a noun. The related verb is grieve. They became separate words when English developed a vphoneme.

Example: She expressed grief at his death. She grieved for her lost husband.

One rarely-used adverb form is grievingly, based on the participle grieving.

Example: He grievingly related the story of the accident.

Answer 3

to grieve; she grieves, they are grieving