ration (n.)

1550, "reasoning," later, "relation of one number to another" (1660s), then "fixed allowance of food" (1702, often rations, from French ration in this sense), from Latin rationem (nominative ratio) "reckoning, numbering, calculation; business affair, procedure," also "reason, reasoning, judgment, understanding," from rat-, past participle stem of reri "to reckon, calculate," also "think" (from PIE root *re- "to reason, count"). The military pronunciation (rhymes with fashion) took over from the preferred civilian pronunciation (rhymes with nation) during World War I.

"put (someone) on a fixed allowance," 1859, from ration (n.); sense of "apportion in fixed amounts" is from 1870. Related: Rationed; rationing.