My dad has a bump the size of about a large grape under the left jaw. Is this a tumor?

possible it's cancer...but sounds more like a goiter to me (enlarged thyroid). in any case, i wouldn't fool around with it...have him see a doctor. sometimes mere days can make a difference in curing these type of things.

This "bump" could be a variety of things, some of which are serious. It could be a tumor, swollen glands, etc. You will not know until he goes to the doctor and has it checked out. This should be done soon.

Most likely it is a plugged salivary duct or salivary stone. Best to get it checked.

Your brief history guide me to left submandibular salivary gland disease . You Must declare : 1 - How long does he have this mass ? 2 - Is there any relations between feeding and it's size or crampy pain (pain that is induced specially by sour food) ? 3 - Does your father has any previous history of head and neck malignancy ? 4 - Is there any fixation to the surrounding tissues ( Bone , Skin , . . . ) ? 5 - How is his lip motions ? is it all right or not ? Depending on the above questions I can help you to determine it's entity . It may be Inflammatory ( calculi , infection , . . . ) or neoplastic ( benign vs malignant ) .