An Etymological Dictionary of Astronomy and Astrophysics

Comparative relation between things, sizes, quantities, numbers, parts, etc.
Math.: A statement of the equality of two ratios.

Etymology (EN): M.E. proporcio(u)n, from
O.Fr. proportion, from L. proportio “comparative relation, analogy,” from the phrase pro portione “according to the relation” (of parts to each other), from pro “for” + portio “part, shar.”

Etymology (PE): Barpâreš, from bar- “on; up; upon; in; into; at; forth; with; near; before; according to” (Mid.Pers. abar; O.Pers. upariy “above; over, upon, according to;” Av. upairi “above, over,” upairi.zəma- “located above the earth;” cf. Gk. hyper- “over, above;” L. super-; O.H.G. ubir “over;” PIE base *uper “over”) + pâr “part, portion, piece” (variants pâréparré “portion, segment (of an orange),” pargâlé, “piece, portion; patch;” (dialects Kermâni pariké “portion, half;” Tabari perik “minute quantity, particle;” Lârestâni pakva “patch;” Borujerdi parru “patch”);
Mid.Pers. pârag “piece, part, portion; gift, offering, bribe;” Av. pāra- “debt,” from par- “to remunerate, equalize; to condemn;” PIE *per- “to sell, hand over, distribute; to assigne;”
Gk. peprotai “it has been granted;” L. pars, as above; Skt. purti- “reward;” Hitt. pars-, parsiya- “to break, crumble”) + -eš suffix.