also: いちごんこじ
noun
person who always has something to say; ready critic
A four-character idiom (yojijukugo) describing someone who feels compelled to offer an opinion on any topic, often with a slightly negative or humorous tone.
彼はまさに一言居士で、どんな話題にも口を挟む。
He is a real 'one-word pundit' who chimes in on every topic.
会議では一言居士の彼がまた長々と意見を述べた。
At the meeting, that ready critic of ours once again gave a lengthy opinion.