An eponym, if you don’t know (and even if you do), is one for whom or which something is or is believed to be named. For example, the Bowie knife or the sandwich (for some Earl of Sandwich) or gerrymandering.
From Wikipedia: “A synonym of ‘eponym’ is namegiver (not to be confused with namesake). Someone who (or something that) is referred to with the adjective eponymous is the eponym of something. An example is: ‘Léon Theremin, known as the eponymous inventor of the theremin.'” The most famous use of the theremin is on the Beach Boys song Good Vibrations.
There are LOTS of examples of upper case eponyms, such as parts of the body (Adam’s apple) or names of diseases (Alzheimer’s disease). I’m more interested in those eponymous words that have “entered in many dictionaries as lowercase when they have evolved a common status, no longer deriving their meaning from the proper-noun origin.” Among the nouns that have achieved this status, many relate to energy. Check out this list:
hertz (Hz), frequency – Heinrich Rudolf Hertz
joule (J), energy, work, heat – James Prescott Joule
newton (N), force – Isaac Newton
ohm (Ω), electrical resistance – Georg Ohm
volt (V), electric potential, electromotive force – Alessandro Volta
watt (W), power, radiant flux – James Watt
Most of these are fairly common terms.
But WHY these? I have no idea. The only eponym list I found comparably lowercase is those which derived from products that were once brand names but are now generic, such as linoleum and videotape.