The term "second string" is commonly used to describe the secondary group of players in a sports team or a group of people who are not the primary choice for a particular task. Antonyms for "second string" include "first string," "top-tier," "elite," "all-star," and "first-rate," which all signify the highest level of skill or competence. Other antonyms include "main," "primary," "core," "primary team," "starting lineup," and "top-notch," which all convey the idea of being the most important or high-quality members of a group. By using these antonyms, one can describe a group of individuals who are revered for their abilities and contributions.