The mile is a unit of length in the imperial unit system with the symbol mi.
It was originally an English unit but was adopted by many countries who all had their own slight variation on definition. The English mile, however, is equal to 63,360 inches, 5280 ft or 1760 yards.
The UK still uses the mile on all roadway signs rather than the kilometre; its SI "equivalent". It used to have the symbol 'm' until SI was established and it was changed to avoid confusion with the unit metre.
The fathom is a unit of length in the imperial unit system and uses the symbol ftm.
One fathom is equal to 6 feet or 1.8288m.
The phrase fathom derives from an old English derivative of a Viking / Danish word "favn" meaning emracing a pair of arms or a pair of oustretched hands.
The fathom is mostly used in the nautical world to describe depths of water.