When we talk about antonyms for the word "re-doubling," the first word that comes to mind is "halving." The concept of halving refers to dividing something into two equal parts or reducing it by 50%. In contrast, re-doubling means to increase by double or to multiply by two. Another antonym for re-doubling is "decreasing" which means to make something smaller or lower in quantity. You can also use "subtracting" as an alternative antonym for re-doubling, which suggests removing something from a given amount or quantity. Finally, "dividing" is an antonym for re-doubling since this term involves splitting something into equal portions.