shark

Concise Oxford English Dictionary © 2008 Oxford University Press:
shark1

▶noun

• 1 a long-bodied cartilaginous marine fish, typically predatory and voracious, with a prominent dorsal fin. [Many species in the subclass Elasmobranchii.]

• 2 a small black SE Asian freshwater fish. [Labeo bicolor and Morulius chrysophekadion.]

• 3 a light greyish-brown moth. [Cucullia umbratica.]

– origin ME: of unknown origin.

Concise Oxford English Dictionary © 2008 Oxford University Press:
shark2

▶noun informal

• 1 a person who exploits or swindles others.

• 2 US an expert in a specified field: a pool shark.

– origin C16: perh. from Ger. Schurke ‘worthless rogue’, influenced by shark1.