Source : Webster's Revised Unabridged Dictionary (1913)

Nonagesimal \Non`a*ges"i*mal\, a. [L. nonagesimus the ninetieth.
   See {Nonagenarian}.] (Astron.)
   Of or pertaining to the ninetieth degree or to a nonagesimal.

Nonagesimal \Non`a*ges"i*mal\, n. (Astron.)
   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.