Epistle Definition of Epistle at Dictionary Epistle definition, a letter, especially a formal or didactic one written communication See . Epistle Definition of Epistle by Merriam Webster Epistle definition is one of the letters adopted as books of the New Testament How to use epistle in a sentence. Epistle An epistle p s l Greek , epistol , letter is a writing directed or sent to a person or group of people, usually an elegant and formal didactic letter The epistle genre of letter writing was c