The prefix for one thousand is "kilo-." Derived from the Greek word "chilioi," which means "thousand," the prefix is commonly used in scientific and mathematical contexts to denote a factor of 1,000. For example, a kilometer (km) is 1,000 meters, and a kilogram (kg) is 1,000 grams. The use of "kilo-" helps simplify measurements and enhances clarity when discussing large quantities. This prefix is part of the International System of Units (SI), ensuring consistent usage in various fields such as science, engineering, and commerce.