An Etymological Dictionary of Astronomy and Astrophysics

A prefix of priority in space or time having especially a meaning of advancing or projecting forward or outward.

Etymology (EN): From L. pro “in favor of, in place of, before, for,” also in some cases from cognate Gk. pro “before, in front of,” both from PIE base *por- “forward, through;” cf. Pers. farâ-, as below; Gk. para- “from beside, against, beyond;” Goth. faura “before,” O.E. fore “before, for, on account of.”

Etymology (PE): Farâ- “forward, along; above, upon, over; before, foremost, opposing, facing,” variant far- intensive prefix “much, abundant; elegantly,” from Mid.Pers. fra-; O.Pers. fra- “forward, forth;” Av. frā, fərā-, fra- “forward, forth; before; excessive” (fratəma- “first, front,” pouruua- “first,” fra-cara- “preceding”);
cf. Skt. prá- “before; forward, in fron,” prathama- “earliest, initial,” pūrva- “first;” Gk. pro; L. pro, as above.