Quaternate refers to something that comes in groups of four. Some synonyms for quaternate include quadruple, tetrad, quartet, and fourfold. These words can be used interchangeably based on the context of the sentence or text. Quadruple is often used to describe something that has increased four times its original amount. Tetrad is commonly associated with a group of four related items or organisms. Quartet is often used in reference to a musical group consisting of four singers or instrumentalists. Fourfold is used to describe something that is four times bigger or greater than its previous size. These synonyms can add variety and precision to one's writing or speech.