www.alphadictionary.com

Given the context of this word in an article I read recently, I thought there was an editing error. Further investigation revealed a classic origin, from Latin, pinna, meaning feather. My guess is pen derived from this word, given the use of quills to place ink to paper. Also, birds are restrained by cutting off the pinion of one wing, just as a person is pinioned by restraining the arms. But the fun does not stop there, as a pinion gear is the smaller of a pair of gears.

Much to my surprise, as the result of a question asking how to draw a "pignon" gear, I have discovered that "pignon" and "pinion" refer to the same object in this sense, although the latter appears much more frequently in English.

Curiously, although my first guess is that "pignon" is from the French, the translation provided online for "rack and pinion" in French is something entirely unrelated etymologically. An online search doesn't yield anything more satisfying (other than a lot of pretty pictures) regarding the gear, and the information that "pignon" also refers to the seeds of a pine, known to me better as "pinyon" or "piñon" (or even "pignola").

Truly a multi-faceted word.