説 （セツ） theory, doctrine, opinion, view, rumour, rumor, gossip, hearsay

説明 （セツメイ） explanation, exposition, description, account, caption, legend

論説 （ロンセツ） article, discourse, dissertation, (written) argument, commentary, editorial, leading article, leader

定説 （テイセツ） established theory, accepted opinion, accepted explanation

遊説 （ユウゼイ） election tour, election campaign, stumping

全国遊説 （ゼンコクユウゼイ） nationwide election campaign

説く （とく） to explain, to preach, to advocate, to persuade, to prevail upon, to reason with, to urge (someone to do)