もちろん
もちろん · mochiron · JLPT N4 · adverb
of course
勿論 = no (勿) + argument (論): no argument needed, of course
Etymology: mochiron is written 勿論 in kanji, where 勿 means must not or without and 論 means debate or discussion. Something so obvious it is beyond discussion is certain. English says the same thing with: it goes without saying.