Diagram showing the relationship between the zenith, the nadir, and different types of horizon. Note that the zenith is opposite the nadir.
From Middle Englishcenyth, from Medieval Latincenit, from Arabicسَمْت (samt, “direction, path”), from the fuller form سَمْت اَلرَّأْس (samt ar-raʾs, “direction of the head”). The -ni- for -m- is sometimes thought to be due to a misreading of the three strokes, which is plausible, though it could be a mere phonetic approximation.
1638 Herbert, Sir Thomas Some years travels into divers parts of Asia and Afrique
The 12 day wee had the wind high and large ſo that in two dayes ſaile we made the Sunne our Zenith or verticall point[…]
1671–1693: Rev. Thomas Jolly, private notebook; printed in: 1895, Henry Fishwick (editor), The Note Book of the Rev. Thomas Jolly: A.D. 1671–1693. Extracts from the Church Books of Altham and Wymondhouses, 1649–1725. And an Account of the Jolly Family of Standish, Gorton, and Altham, page 44
In this 10th m. appeared that prodigious Comett the tayl whereof was like the blade of a double edged sword, and reached almost from the horizon to the zenith.
The translations below need to be checked and inserted above into the appropriate translation tables, removing any numbers. Numbers do not necessarily match those in definitions. See instructions at Wiktionary:Entry layout § Translations.