Definitions of shark:

noun: any of numerous elongate mostly marine carnivorous fishes with heterocercal caudal fins and tough skin covered with small toothlike scales
noun: a person who is unusually skilled in certain ways
Example: "A card shark"
noun: a person who is ruthless and greedy and dishonest
verb: play the shark; act with trickery
verb: hunt shark
name: A surname (very rare: popularity rank in the U.S.: #60333)