Definitions of sum:

• noun:   the whole amount
• noun:   a quantity obtained by addition
• noun:   the final aggregate

  Example: "The sum of all our troubles did not equal the misery they suffered"

• noun:   a quantity of money

  Example: "He borrowed a large sum"

• noun:   the basic unit of money in Uzbekistan
• noun:   the choicest or most essential or most vital part of some idea or experience
• noun:   a set containing all and only the members of two or more given sets
• verb:   be a summary of

  Example: "The abstract summarizes the main ideas in the paper"

• verb:   determine the sum of
• name:  A surname (very rare: popularity rank in the U.S.: #19407)