nonagesimal

CIDE DICTIONARY

nonagesimal, a. [L. nonagesimus the ninetieth. See Nonagenarian.].

 Of or pertaining to the ninetieth degree or to a nonagesimal.  [1913 Webster]

nonagesimal, n. 

 The middle or highest point of the part of the ecliptic which is at any given moment above the horizon. It is the ninetieth degree of the ecliptic, reckoned from the points in which it is intersected by the horizon.  [1913 Webster]