A "letter to the editor" refers to a piece of writing sent to a newspaper or magazine, expressing the opinion of a reader on a particular topic. There are several synonyms for this phrase, including "editorial comment," "reader feedback," "opinion piece," "written response," and "correspondence to the editor." Some other phrases that can be used to refer to a "letter to the editor" include "write-up," "feedback submission," or "submitted comment." Overall, these synonyms all refer to a form of written communication where readers share their thoughts and feelings on a particular subject with a wider audience.