The term "shoo-in" is defined as a sure winner or a certain choice. Antonyms for this could include phrases such as "underdog," "long shot," or "doubtful contender." These phrases represent a level of uncertainty or unlikelihood, indicating that the outcome is not guaranteed. Other antonyms might include "neck-and-neck," "close call," or "toss-up," which describe situations where the outcome is difficult to predict and could go either way. Using these antonyms can add complexity and nuance to language and help to convey a greater range of meanings in communication.