oktan.
/ˈɒktə/, U.S. /ˈɑktə/ Meteorology and Aeronautics.
A unit used in expressing the extent of cloud cover, equal to one-eighth of the sky.
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okta1950
1950 Meteorol. Gloss. (Meteorol. Office) (new ed.) Amendment List No. 4. 7 Okta, unit, equal to area of one eighth of the sky, used in specifying cloud amount.
1957 Meteorol. Gloss. (Meteorol. Office) (new ed.) iv. 35 From January 1, 1949, cloud amount has been observed and reported in oktas or eighths of sky covered, code figure 0 representing a clear sky, 1 representing 1 okta (eighth) of sky covered or less, but not zero, 2 representing 2 oktas (eighths), and so on..8 representing 8 oktas (eighths) (sky completely covered), and 9 representing sky obscured or cloud amount cannot be estimated.
1977 ‘J. le Carré’ Honourable Schoolboy xviii. 455 Cloud is anticipated at six to seven okta.
1979 R. Prest F4 Phantom xiii. 130 The Boeing 737 punches through the few remaining octas of cloud on its final approach.
1993 Irish Times (Nexis) 8 Nov. 2 A total cover of six okta may consist of two separate layers five okta of low level cumulus cloud with four okta of altostratus several thousand feet above it.
This entry has been updated (OED Third Edition, March 2004; most recently modified version published online March 2022).
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n.1950