An Etymological Dictionary of Astronomy and Astrophysics

1. Going on at the same rate and exactly together. Compare → simultaneous.
   

2. Having the same period and phase of oscillation or cyclic movement.

Etymology (EN): From L. synchronus “simultaneous,” from Gk. synchronos “happening at the same time,” from → syn- “together”

• khronos “time.”

Etymology (PE): Hamgâm literally “at the same pace,” from ham-, → syn-, + gâm “step, pace,” Mid.Pers. gâm, O.Pers. gam- “to come; to go,” Av. gam- “to come; to go,” jamaiti “goes,” Mod.Pers. âmadan “to come,” Skt. gamati “goes,” Gk. bainein “to go, walk, step,” L. venire “to come,” Tocharian A käm- “to come,” O.H.G. queman “to come,” E. come; PIE root *gwem- “to go, come.”