The Collaborative International Dictionary of English v.0.48:
Plunge \Plunge\, v. i.
1. To thrust or cast one's self into water or other fluid; to
submerge one's self; to dive, or to rush in; as, he
plunged into the river. Also used figuratively; as, to
plunge into debt.
Forced to plunge naked in the raging sea. --Dryden.
To plunge into guilt of a murther. --Tillotson.
2. To pitch or throw one's self headlong or violently
forward, as a horse does.
Some wild colt, which . . . flings and plunges.
3. To bet heavily and with seeming recklessness on a race, or
other contest; in an extended sense, to risk large sums in
hazardous speculations. [Cant]
Plunging fire (Gun.), firing directed upon an enemy from an