This was the first in a string of rhyming words submitted to my site. So, how exactly did duck mean both "waterfowl" and "to lower your head or body"? The reason can be traced back to the word ducan, which meant "to dive", and was descended from the Proto-Indo-European word dukjan. Ducan was then mangled into duce in Old English, and still meant "to dive". It kept this original definition through its entire usage, but right around the point when duce became duck, people got tired of saying elan, which was the ugly and cumbersome PIE-descended word for "duck" at the time, and decided to use the same word for two things because 1) it was easier and 2) a duck has to "duck" underwater to feed, so the verb kind of became the noun in that instance. Mostly in the twentieth and nineteenth centuries, a bunch of military terms were derived from duck, including sitting duck and duck and cover. Lame Duck referred to a stockbroker who couldn't pay his debts, and as a word evolved from there. Duck also means a type of cloth, but that's a different story.
Adam Aleksic, a rising sophomore studying linguistics and government at Harvard University, has been described as the internet's sixth most famous etymologist. He also has disturbing interests in politics, vexillology, geography, board games, conlanging, and law.