Real Dictionary

shark
countable noun: If you refer to a person as a shark, you disapprove of them because they trick people out of their money by giving bad advice about buying, selling, or investments.
variable noun: A shark is a very large fish. Some sharks have very sharp teeth and may attack people.

shark in American English 1
a person who victimizes others, as by swindling or cheating
to get or live by fraud or stratagems
noun: any of a group of elongate elasmobranch, mostly marine fishes, certain species of which are large, voracious, and sometimes dangerous to humans

shark in American English 2
any of various orders of cartilaginous fishes that are usually large and mostly marine, having a tough, spiny, usually slate-gray skin, separate lateral gill openings, and a slender, rounded body with the mouth on the underside: most sharks are fish-eater
intransitive verb: to live by shifts and stratagems
noun: a person who preys greedily on others, as by cheating or usury
transitive verb: to obtain by trickery or fraud; steal

shark in British English 1
noun: any of various usually ferocious selachian fishes, typically marine with a long body, two dorsal fins, rows of sharp teeth, and between five and seven gill slits on each side of the head

shark in British English 2
noun: a person who preys on or victimizes others, esp by swindling or extortion
verb: to obtain (something) by cheating or deception