The letter "C" is a commonly used letter in the English language. There are several words that can be used as synonyms for the letter "C." These include "cipher," "character," "count," "calculation," "computation," and "cypher." Each of these words has a slightly different connotation, but they all refer to the same concept of the third letter of the English alphabet. Synonyms can be helpful when writing or speaking to avoid repetition and to add variety to one's language use. It is essential to have a broad vocabulary and a strong understanding of synonyms to be able to communicate effectively and eloquently.