From Longman Dictionary of Contemporary Englishon-messageˌon-ˈmessage adjective [not before noun], adverb a politician who is on-message says things that are in agreement with the ideas of his or her political party, especially when it appears that he or she is not thinking enough about these ideas OPP off-messageFrom Longman Business Dictionaryon-messageˌon-ˈmessage adjective, adverb a politician who is on-message says things that are in agreement with the ideas and policies of the political party they belong to → compare off-message