The ell is a unit of length and originates from historic England and uses the symbol ell.
The ell usually measured 45in or 1.143m but was origally a "cubit" - which was the length from your elbow to the tip of your fingers and literally translated from the word "arm". It was mostly used in the tailoring world when buying and selling textiles.
Although now obsolete, the word "ell" still survives in the English word "elbow".
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.