əˈdɪʃən sʌˈmeɪʃən the arithmetic operation of summing; calculating the sum of two or more numbers the summation of four and three gives seven a concluding summary (as in presenting a case before a law court) the final aggregate the sum of all our troubles did not equal the misery they suffered (physiology) the process whereby multiple stimuli can produce a response (in a muscle or nerve or other part) that one stimulus alone does not produce