The furlong is a unit of length in the imperial unit system and uses the symbol fur.
One furlong is equal to 1/8 mile, 660 feet, 220 yards, 40 rods, 10 chains or ≈ 201m.
The furlong was a term used to describe the legnth of a furrow in one acre of a ploughed open field (communal field). It now only really remains in the world of horse-racing in UK, Ireland, Canada and the US.
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.