The word incumbent was borrowed in the fifteenth century from the Medieval Latin present active participle incumbens, which meant "holding an office" (especially for ecclesiastical positions) but more literally translates to "reclining". The idea, presumably, was that incumbents figuratively "lean" on their current positions. The infinitive of incumbens is incumbere, which was composed of the prefix in-, meaning "on" (from Proto-Indo-European en) and the root cumbere, "to lie down". That comes from Proto-Italic kubao and Proto-Indo-European kewb, which probably meant something like "sleep". Cumbere has been a pretty prolific word in English, also giving us words like succumb, catacomb, and decubitus; other relatives include cubicle, concubine, succubus, and more.
Hello! I'm Adam Aleksic, a sophomore studying government and linguistics at Harvard University, where I co-founded the Harvard Undergraduate Linguistics Society. In addition to etymology, I also really enjoy politics, vexillology, geography, board games, conlanging, and law.