From Longman Dictionary of Contemporary Englishsharkshark /ʃɑːk $ ʃɑːrk/ ●●○ noun [countable] 1 
HBFa large sea fish with several rows of very sharp teeth that is considered to be dangerous to humans Sharks were circling around our boat.shark-infested waters (=waters where there are a lot of sharks)2 informalTRICK/DECEIVE someone who cheats other people out of moneypool/card shark (=someone who uses their skill at pool or cards to cheat other players out of money) → loan shark
HBFa large sea fish with several rows of very sharp teeth that is considered to be dangerous to humans Sharks were circling around our boat.shark-infested waters (=waters where there are a lot of sharks)2 informalTRICK/DECEIVE someone who cheats other people out of moneypool/card shark (=someone who uses their skill at pool or cards to cheat other players out of money) → loan sharkExamples from the Corpus
shark• Yes, beaming, grinning like a shark.• The skyline, from any part of this magical plateau, was toothed like the jaw of a shark.• The whales favour large prey, including squid, cod and sharks.• This time its offerings include a dead shark floating in a tank of formaldehyde.• It was only a small shark about three feet long so I ignored it and began the survey.• Unlike sharks, they don't waste energy preventing themselves from sinking.• The currents helped him, but those currents are filled with sharks.• You got your freezing water, your sharks and your hepatitis.pool/card shark• The titles are stacking up like the poker chips of a red-hot card shark.• Where were the saloons and the gunslingers and the professional card sharks?From Longman Business Dictionarysharkshark /ʃɑːkʃɑːrk/ noun [countable] informalFINANCE someone who cheats other people out of money, especially by giving bad financial adviceNever do business with these sharks. → loan sharkOrigin shark 1. (1400-1500) Origin unknown. 2. (1500-1600) Probably from German schurke “bad man”; influenced by → SHARK1 