Plunge, dive, pitch are comparable when they mean to throw or cast oneself or to be thrown or cast forward or downward with force or impetuosity into or as if into deep water.
Plunge carries a more obvious implication than the others of the force with which one throws oneself or is thrown, but it does not always suggest a penetration of deep water; it may imply entrance into any penetrable medium, especially one that suggests a being lost to view, or into a state or condition in which one is overwhelmed or immersed, or into a course which marks a deep descent, a complete change, or a distinct involvement.
Dive, though it implies an action very similar to that indicated by plunge, usually suggests deliberation or, at least, consciousness of an aim, more skill in execution, and less heaviness and more grace; thus, “he dived into the sea” usually implies intent where “he plunged headlong into the sea” may suggest either intent, accident, or impulsion by some force.
Pitch (see also THROW ) is often used instead of plunge to imply a falling forward and downward usually without intent or design.
The term also is often used in reference to the alternate forward and backward plunging of a ship in a storm as distinguished from rolling or tossing from side to side.