An Etymological Dictionary of Astronomy and Astrophysics

Prefix meaning “to, toward, addition to, near,” from L. ad “to, toward.” It is modified to ac- or af- or ag- or al- etc. according to the following consonant.

Etymology (EN): Cognate with E. at, from O.E. æt “near, by, at”; compare with O.N., Goth. at, O.Fris. et, O.H.G. az, Skt. adhi “near,” PIE *ad- “to, near, at”.