Wiktionary:Word of the day/2024/January 25

1. A literary composition in the form of a letter or series of letters, especially one in verse.
2. (chiefly literary or humorous) A letter, especially one which is formal or issued publicly.
   1. (specifically, historical) Chiefly with a qualifying word, as in epistle dedicatory: a letter of dedication addressed to a patron or reader published as a preface to a literary work.
3. (Christianity)
   1. One of the books of the New Testament which was originally a letter issued by an apostle to an individual or a community.
   2. An extract from a New Testament epistle (sense 3.1) or book other than a gospel which is read during a church service, chiefly the Eucharist.

epistle v

1. (transitive)
   1. (chiefly literary or humorous) To write (something) in, or in the form of, a letter.
   2. (chiefly literary or humorous, archaic) To write a letter to (someone).
   3. (rare) To write (something) as an introduction or preface to a literary work; also, to provide (a literary work) with an introduction or preface.
2. (intransitive, chiefly literary or humorous)
   1. To write a letter.
   2. To communicate with someone through a letter.

Today is celebrated by some Christian churches as the Feast of the Conversion of Saint Paul the Apostle. Thirteen of the epistles in the New Testament of the Bible identify Paul as the writer.