some / sum are similar-sounding terms with different meanings (referred to as homophones). To better understand the differences, see below for definitions, pronunciation guides, and example sentences using each term. 👇
some: (adjective) quantifier; used with either mass nouns or plural count nouns to indicate an unspecified number or quantity. (adjective) relatively much but unspecified in amount or extent. (adjective) relatively many but unspecified in number. (adjective) remarkable.
sum: (noun) a quantity of money. (noun) a quantity obtained by the addition of a group of numbers. (noun) the final aggregate. (noun) the whole amount.
some: s·AH·m
sum: s·AH·m
(Examples are Wikipedia snippets under the CC ShareAlike 3.0 license. Definitions drawn from WordNet.)