The word "summate" means to add up or total something, but its antonyms are words that signify subtraction or restitution. A few antonyms for "summate" are deduct, remove, subtract, and reduce. When we use the word "deduct," we mean to subtract an amount from a total. For example, if we deduct taxes from our earnings, we have the net earnings left. In contrast, if we "remove" someone from a list, we erase or eliminate them from the roster. If we use the word "subtract," we have to decrease a particular value from another value. Finally, the word "reduce" means to make something smaller or less.