n. [ Of uncertain origin; perhaps through OF. fr. carcharus a kind of dogfish, Gr. karchari`as, so called from its sharp teeth, fr. ka`rcharos having sharp or jagged teeth; or perhaps named from its rapacity (cf. Shark, v. t. & i.); cf. Corn. scarceas. ] 1. (Zool.) Any one of numerous species of elasmobranch fishes of the order Plagiostomi, found in all seas. [ 1913 Webster ]

☞ Some sharks, as the basking shark and the whale shark, grow to an enormous size, the former becoming forty feet or more, and the latter sixty feet or more, in length. Most of them are harmless to man, but some are exceedingly voracious. The man-eating sharks mostly belong to the genera Carcharhinus, Carcharodon, and related genera. They have several rows of large sharp teeth with serrated edges, as the great white shark (Carcharodon carcharias or Carcharodon Rondeleti) of tropical seas, and the great blue shark (Carcharhinus glaucus syn. Prionace glauca) of all tropical and temperate seas. The former sometimes becomes thirty-six feet long, and is the most voracious and dangerous species known. The rare man-eating shark of the United States coast (Carcharodon Atwoodi) is thought by some to be a variety, or the young, of Carcharodon carcharias. The dusky shark (Carcharhinus obscurus) is a common species on the coast of the United States of moderate size and not dangerous. It feeds on shellfish and bottom fishes. [ 1913 Webster ]

The original 1913 Webster also mentioned a “smaller blue shark (C. caudatus)”, but this species could not be found mentioned on the Web (August 2002). The following is a list of Atlantic Ocean sharks:
* * * * * * * * * * * * * * * *
Common and Scientific Names of Atlantic Sharks
* * * * * * * * * * * * * * * *
from “Our Living Oceans 1995” (published by the National Printing Office):
NMFS. 1999. Our Living Oceans. Report on the status of U.S. living marine resources, 1999. U.S. Dep. Commer., NOAA Tech. Memo. NMFS-F/SPO-41, on-line version, https://web.archive.org/web/20170513162849/http://spo.nwr.noaa.gov/olo99.htm.

(the following list is found at at https://web.archive.org/web/20010614193559/http://spo.nwr.noaa.gov/app5.pdf)
(1) Pelagic Sharks

Thresher shark (Alopias vulpinus)
Bigeye thresher (Alopias superciliosus)
Oceanic whitetip shark (Carcharhinus longimanus)
Sevengill shark (Heptrachias perlo)
Sixgill shark (Hexanchus griseus)
Bigeye sixgill shark (Hexanchus vitulus)
Shortfin mako (Isurus oxyrinchus)
Longfin mako (Isurus paucus)
Porbeagle (Lamna nasus)
Blue shark (Prionace glauca)

(2)Large Coastal Sharks

Sandbar shark (Carcharhinus plumbeus)
Reef shark (Carcharhinus perezi)
Blacktip shark (Carcharhinus limbatus)
Dusky shark (Carcharhinus obscurus)
Spinner shark (Carcharhinus brevipinna)
Silky shark (Carcharhinus falciformis)
Bull shark (Carcharhinus leucas)
Bignose shark (Carcharhinus altimus)
Galapagos shark (Carcharhinus galapagensis)
Night shark (Carcharhinus signatus)
White shark (Carcharodon carcharias)
Basking shark (Cetorhinus maximus)
Tiger shark (Galeocerdo cuvier)
Nurse shark (Ginglymostoma cirratum)
Lemon shark (Negaprion brevirostris)
Ragged-tooth shark (Odontaspis ferox)
Whale shark (Rhincodon typus)
Scalloped hammerhead (Sphyrna lewini)
Great hammerhead (Sphyrna mokarran)
Smooth hammerhead (Sphyrna zygaena)

(3) Small Coastal Sharks

Finetooth shark (Carcharhinus isodon)
Blacknose shark (Carcharhinus acronotus)
Atlantic sharpnose shark (Rhizoprionodon erraenovae)
Caribbean sharpnose shark (Rhizoprionodon porosus)
Bonnethead (Sphyrna tiburo)
Atlantic angel shark (Squatina dumeril)
[ PJC ]

2. A rapacious, artful person; a sharper. [ Colloq. ] [ 1913 Webster ]

3. Trickery; fraud; petty rapine; as, to live upon the shark. [ Obs. ] South. [ 1913 Webster ]

Basking shark,
Liver shark,
Nurse shark,
Oil shark,
Sand shark,
Tiger shark, etc. See under Basking, Liver, etc. See also Dogfish, Houndfish, Notidanian, and Tope. --
Gray shark, the sand shark. --
Hammer-headed shark. See Hammerhead. --
Port Jackson shark. See Cestraciont. --
Shark barrow, the eggcase of a shark; a sea purse. --
Shark ray. Same as Angel fish (a), under Angel. --
Thrasher shark or
Thresher shark, a large, voracious shark. See Thrasher. --
Whale shark, a huge harmless shark (Rhinodon typicus) of the Indian Ocean. It becomes sixty feet or more in length, but has very small teeth. [ 1913 Webster ]

v. t. [ Of uncertain origin; perhaps fr. shark, n., or perhaps related to E. shear (as hearken to hear), and originally meaning, to clip off. Cf. Shirk. ] To pick or gather indiscriminately or covertly. [ Obs. ] Shak. [ 1913 Webster ]

v. i. [ imp. & p. p. Sharked p. pr. & vb. n. Sharking. ] 1. To play the petty thief; to practice fraud or trickery; to swindle. [ 1913 Webster ]

Neither sharks for a cup or a reckoning. Bp. Earle. [ 1913 Webster ]

2. To live by shifts and stratagems. Beau. & Fl. [ 1913 Webster ]

n. One who lives by sharking. [ 1913 Webster ]

n. Petty rapine; trick; also, seeking a livelihood by shifts and dishonest devices. [ 1913 Webster ]