The retention index is a measure of how well a substance sticks to a medium. There are many synonyms for the word retention index, including retention time, elution time, adsorption time, and peak identification. These terms are used to describe the amount of time it takes for a substance to be retained by a stationary phase. This is important in chromatography, where the goal is to separate a mixture of compounds based on their different retention times. By using different retention indices, scientists can determine the identity and purity of different compounds in a mixture. Overall, these synonyms play a crucial role in chemical analysis and research.