There are many synonyms for the phrase "one and the other." Some of the most common include "both," "each other," "either," "neither," "the pair," and "the two." These synonyms can be used interchangeably with "one and the other" in many situations, such as when discussing two different options, describing a relationship between two people or objects, or comparing and contrasting two different ideas or perspectives. When choosing which synonym to use, it's important to consider the context and tone of the conversation or writing, as well as any specific connotations or implications that may be associated with each word.