ration has 1 distinct synonym spread across 1 of its 4 senses. Each sense below keeps its own list, because a synonym belongs to a meaning and not to a word: swapping one sense's substitute into another sense's sentence is how a thesaurus makes writing worse. WordNet records no antonym for it — antonymy is a relation between word forms rather than concepts, so it is deliberately sparse.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
the food allowance for one day (especially for service personnel)
“the rations should be nutritionally balanced”
a fixed portion that is allotted (especially in times of scarcity)
Synonyms, antonyms and the broader and narrower relations for ration come from Princeton University’s WordNet. Full sources and licences.
restrict the consumption of a relatively scarce commodity, as during war
“Bread was rationed during the siege of the city”
distribute in rations, as in the army
“Cigarettes are rationed”