Sum  —n. 1 total resulting from addition. 2 amount of money (a large sum). 3 a arithmetical problem. B (esp. Pl.) Colloq. Arithmetic work, esp. Elementary. —v. (-mm-) find the sum of.  in sum in brief. Sum up 1 (esp. Of a judge) give a summing-up. 2 form or express an opinion of (a person, situation, etc.). 3 summarize. [latin summa]