There are various synonyms for the phrase "become cool" that can be used to describe a popular trend or an admired individual. Some examples of synonyms for "become cool" include "be in vogue," "attain hipness," "achieve trendiness," "attain trend status," "become fashionable," "gain popularity," "attain hip status," and "be trendy." All these synonyms describe a similar idea of achieving a certain level of desirability or attractiveness to a particular group or among society in general. Using these synonyms can help add variety to writing or conversation while conveying the same meaning.