The point on the celestial sphere directly overhead at a particular location; = zenithn. A.1a.
1585
The Azimuthes..are those which are drawne cutting all the almicantares meeting altogither at one point..: which point I call the zenith point of the reete.
J. Blagrave, Math. Iewelii. xvi.
a1652
Only in North Declinations the Equinoctiall goes nearer the Zenith point, in South it goes further of.
S. Foster, Elliptical Horologiography (1654) 63
1829
The zenith sector..can be used only on the meridian; and its measures are referred to the zenith point of the place of observation.
W. Pearson, Practical Astronomyvol. II. 531
1950
From the known positions of the star images in the celestial sphere, the co-ordinates of the zenith point may be computed.
Technical Data Digest January 7/3
2011
The observer..is at O and the plane containing the circle NESW is again the horizon with Z the zenith point.
P. Duffet-Smith & J. Zwart, Pract. Astron. with Calculator (ed. 4) xviii. 35
zenith point typically occurs fewer than 0.01 times per million words in modern written English.
zenith point is in frequency band 2, which contains words occurring between 0.001 and 0.01 times per million words in modern written English. More about OED's frequency bands
Frequency data is computed programmatically, and should be regarded as an estimate.
Frequency of zenith point, n., 1760–2010
* Occurrences per million words in written English
Historical frequency series are derived from Google Books Ngrams (version 2), a data set based on the Google Books corpus of several million books printed in English between 1500 and 2010.
The overall frequency for a given word is calculated by summing frequencies for the main form of the word, any plural or inflected forms, and any major spelling variations.
For sets of homographs (distinct entries that share the same word-form, e.g. mole, n.¹, mole, n.², mole, n.³, etc.), we have estimated the frequency of each homograph entry as a fraction of the total Ngrams frequency for the word-form. This may result in inaccuracies.
Smoothing has been applied to series for lower-frequency words, using a moving-average algorithm. This reduces short-term fluctuations, which may be produced by variability in the content of the Google Books corpus.
Decade
Frequency per million words
1760
0.017
1770
0.014
1780
0.014
1790
0.013
1800
0.012
1810
0.011
1820
0.014
1830
0.014
1840
0.016
1850
0.016
1860
0.018
1870
0.017
1880
0.015
1890
0.012
1900
0.011
1910
0.0091
1920
0.0078
1930
0.0061
1940
0.0058
1950
0.0049
1960
0.0044
1970
0.0044
1980
0.0043
1990
0.0043
2000
0.0039
2010
0.0036
Originally published as part of the entry for zenith, n. & adj.