1. To stick out from the surroundings or to make something do this: The wreckage of the ship that sank into the ocean during the terrible storm was seen protruding from the water.

Jane's rebellious child son protruded his tongue at her when she told him to go wash his hands before he came to the dinner table.

The fin of the shark protruded from the water near Adam's boat.

2. To thrust forward; to cause to project outward: The dentist told Mary that her teeth protrude too much and so she would have to wear braces to readjust them.
3. To shoot out or forth; to be thrust forward; to extend beyond a limit; to project: Karl lost his handkerchief because it protruded too far out of the back pocket of his pants when he was going for a walk.
4. Etymology: from Latin protrudere, "to thrust forth"; from pro, "forward" + trudere, "to thrust, to extend, to push".