An Etymological Dictionary of Astronomy and Astrophysics

Physics: The line or curve described by an object moving through space.
Math.: A curve or surface that cuts all of a given family of curves or surfaces at the same angle.

Etymology (EN): From Mod.L. trajectoria, from feminine of trajectorius “of or pertaining to throwing across,” from L. trajectus “thrown over or across,” p.p. of trajicere “throw across,” from L. → trans- “across” + icere, combining form of jacere “to throw,” → eject.

Etymology (PE): Tarâyešâné, from tarâ- “across,” → trans-,

• -y- epenthetic + ešân, present stem of ešândan, → eject, + relation suffix -é.