We’re on the downswing now!
Today’s word: net.
Net has two definitions, netting and remaining (like net income after taxes). The first net comes from the Old English word net (believe it or not) and before that, the Proto Germanic natjan, and Proto Indo European [http://colfa.utsa.edu/drinka/pie/pie.html] ned-, twist or knot. The other net showed up in the early sixteenth century and originally it meant clean or neat (the monetary origin is probably from Italian influence as their word for neat, netto, meant “remaining after deductions). It comes from the Old French net (yes, this is different from the Old English one), which meant clean or pure, and classical Latin nitere, to shine. It also has a Proto Indo European origin word: nei-. Which leaves us to assume that the reason these two words are spelled the same is because people dropped the a in the neat when they were talking about deductions. Because things weren’t confusing enough.
Tony Jebson’s page on the Origins of Old English
University of Texas at Austin Linguistic Research Center