means A cartilaginous, predatory fish — sleek, toothy, and built to hunt — or, figuratively, a ruthless person who preys on others, especially in money or cards.

from The fish-name 'shark' surfaces in English in the 16th century, and nobody is quite sure where it swam in from — one leading guess connects it to German 'Schurke,' a scoundrel or villain, which would make the predator named after the cheat rather than the other way round. The human 'shark' (a swindler, a card-sharp, a loan shark) grew up alongside it, the two senses feeding each other across the centuries until 'loan shark' and 'pool shark' became the everyday faces of a word whose deepest origins remain, fittingly, murky water.