tetragon
An aspect of two planets with regard to the Earth when they are distant from each other ninety degrees, or a quarter-circle.
In the horoscope of Christ's nativity.[…]Whether a trigon or no, this tetragon I am sure there was.
Where it comes from
From Ancient Greek τετράγωνος (tetrágōnos). By surface analysis, tetra- + -gon.
Adapted from the Wiktionary entry tetragon (CC BY-SA 4.0).