The term 'SHARK'S FOE' can be solved by the three letter word 'JET'. A JET is a type of aircraft that is powered by an engine and is capable of reaching high speeds. Jets are often used by militaries for combat and reconnaissance missions, and they can also be used for civilian purposes such as air travel. In terms of a shark's foe, jets can be used to scare away sharks from areas where people are swimming or surfing.