For such a curious word like zenith, it comes as little shock that there are several proposed origins. This word, meaning "apex of power or success", earlier meant "time when a celestial object is directly over an observer". The later definition also persists to today, but less so. This is generally acknowledged to have come from the French word cenith, which comes from the Latin term cenit. Here the origin theories diverge. The more pleasing notion is that from here it directly goes back to Arabic samt, "direction", which would go back to either Aramaic symt or Arabic smt, in any case tracing back to Afro-Asiatic. The second theory is that zenith was only slightly influenced by the Arabic word through folk etymology, and it in fact comes from the earlier Latin word semita, "path", from the Proto-Indo-European root mei, or "to change". As with all etymology, we'll never know for sure until we get a time machine.
Adam Aleksic, a freshman studying linguistics at Harvard University, has been described as the internet's sixth most famous etymologist. He has disturbing interests in words, vexillology, geography, board games, limericks, and law, and he loves writing about himself in the third person.
The Etymology Nerd