An Etymological Dictionary of Astronomy and Astrophysics

General: Characterized by or consisting of two parts or components.
Math.: Of or relating to a system of numeration having 2 as its base.
Astro.: Physically associated pair of astronomical objects.

Etymology (EN): Binary, from L.L. binarius, from bini “two-by-two,” from bis “twice, two times;” cf. Av. biš- “twice,” bi- “two,” Mod.Pers. do “two,” PIE *dwo- “two.”

Etymology (PE): Dorin, from Mid.Pers. dorin “double, pair,” from do (Av. dva-, Skt. dvi-, Gk. duo, L. duo, E. two, Der. zwei, Fr. deux) “two” + rin “time, turn.”
Dodoyi “two-by-two,” from do, → two.