Webster's Revised Unabridged Dictionary · 1913

Epistle

Epistle , noun

[Old English epistle, epistel, Anglo-Saxon epistol, pistol, Latin epistola, from Greek {not transcribed} anything sent by a messenger, message, letter, from {not transcribed} to send to, tell by letter or message; 'epi` upon, to + {not transcribed} to dispatch, send; compare Old French epistle, epistre, French épître. See Stall.]

1.
A writing directed or sent to a person or persons; a written communication; a letter; -- applied usually to formal, didactic, or elegant letters.
A madman's epistles are no gospels. — Shakespeare
2.
(Ecclesiastical) One of the letters in the New Testament which were addressed to their Christian brethren by Apostles.
One sees the pulpit on the epistle side. — R. Browning
Collocations (1)
Epistle side , the right side of an altar or church to a person looking from the nave toward the chancel.

Epistle , transitive verb

To write; to communicate in a letter or by writing. [Obsolete] — Milton