The phrase "the well-to-do" refers to those who are affluent or prosperous. There are many synonyms for this term, including "the wealthy," "the rich," "the prosperous," "the affluent," and "the well-heeled." Other synonyms include "the moneyed," "the upper crust," "the elite," "the privileged," and "the gentry." These terms all describe people who have a high level of financial comfort and are not struggling to make ends meet. It's important to note that while these words may be used interchangeably, they can have slightly different connotations and may be preferred by different speakers depending on their intended tone or audience.