PROPORTION'S PART

The noun proportion was first used in English in a 1382 translation of the Holy Bible by theologist John Wycliffe, and the verb came shortly afterwards. At that point it was spelled proporcyon; after a few hundred years alternating in usage with proporcioun and proportion, the latter won out. The word comes from Old French proporcion and Latin proportionem, both of which meant "measurement". Proportionem in turn came from the phrase pro portione, which is best translated as  "according to the relation" but literally means "for part": pro meant "for" (and traces to Proto-Indo-European per, or "before") and portione is the ablative singular of portionem, which meant "proportion" or "part" (and derives from Proto-Indo-European pere, which meant "to allot").