The act of plunging or submerging

A dive, leap, rush, or pitch into (into water)

“A plunge into the sea”

A swimming pool

To thrust into liquid, or into any penetrable substance; to immerse.

“to plunge the body into water”

To cast, stab or throw into some thing, state, condition or action.

“to plunge a dagger into the breast;   to plunge a nation into war”

To baptize by immersion.