Synonyms for Plunger (same or very similar meaning)
WordNet sense 1 (someone who risks losses for the possibility of considerable gains):
speculatorWordNet sense 2 (someone who dives (into water)):
diverWordNet sense 3 (hand tool consisting of a stick with a rubber suction cup at one end; used to clean clogged drains):
plumber's helperWordNet sense 4 (mechanical device that has a plunging or thrusting motion):
pistonFrom the ODE community, based on WordNetadd/edit