There are numerous synonyms that can be used in place of the word "millionths." Some of these synonyms include millionth part, millionth proportion, and millionth share. Further, fractional and decimal representations can be used, such as 0.000001 or 1/1,000,000. Other synonyms for this term include infinitesimal, tiny, and miniscule. Additionally, in mathematical terms, the word micro can be used to represent millionths, as in microsecond or micrometer. These synonyms can be utilized based on the context in which they are being used, allowing for flexibility in expressing numerical values.