Dictionary.com
definitions

encyclical

[en-sik-li-kuh l, -sahy-kli-]
noun
  1. Roman Catholic Church. a letter addressed by the pope to all the bishops of the church.
adjective
  1. (of a letter) intended for wide or general circulation; general.
Also en·cyc·lic.

Origin of encyclical

1610–20; < Late Latin encyclicus (< Greek enkýklios, with -icus -ic for -ios, equivalent to en- en-2 + kýkl(os) circle, cycle + -ios adj. suffix) + -al1
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018
British Dictionary definitions for encyclical

encyclical

noun
  1. a letter sent by the pope to all Roman Catholic bishops throughout the world
adjective Also: encyclic
  1. (of letters) intended for general or wide circulation

Word Origin for encyclical

C17: from Late Latin encyclicus, from Greek enkuklios general, from kuklos circle
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
Word Origin and History for encyclical
adj.

in reference to a letter sent by the Pope to all the bishops, 1640s, from Late Latin encyclicus, from Latin encyclius, from Greek enkyklios "in a circle, circular" (see encyclopedia). As a noun, from 1837.

Online Etymology Dictionary, © 2010 Douglas Harper
encyclical in Culture

encyclical

[(en-sik-li-kuhl)]

A letter from the pope to the bishops of the Roman Catholic Church, in which he lays down policy on religious, moral, or political issues.

The New Dictionary of Cultural Literacy, Third Edition Copyright © 2005 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.