a letter, often of protest or criticism, addressed to a specific person, but intended to be brought to public attention.
Origin of open letter
First recorded in 1875–80
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
a letter, esp one of protest, addressed to a person but also made public, as through the press
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