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.
The nanometre is a unit of length and is a multiple of the SI unit metre. It uses the symbol nm.
1 nm is equal to one one-billionth of a metre. (Nano is the prefix for one billionth). It is used to express dimensions on an atomic scale for example a helium atom has a radius of approximately 0.03nm.
The nanometre was previously known as the millimicrometre (or the millimicron).