The most common and most likely answer to this crossword clue is the 10 letter word EQUATORIAL
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More clues leading to the result EQUATORIAL
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The cryptic/wordplay part
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What does EQUATORIAL mean?
EQUATORIAL noun- A kind of telescope mounted so as to have two axes of motion at right angles to each other, one of them parallel to the axis of the Earth, and each carrying a graduated circle, one for measuring declination, and the other right ascension, or the hour angle, so that the telescope may be directed, even in the daytime, to any star or other object whose right ascension and declination are known.
- Of, near, or relating to the equator
- Perpendicular to the plane of a ring