The Eoyeongcheong (御營廳) was originally an elite garrison that guarded the king. Founded as the Eoyeong corps after the Injo coup and promoted to one of the Three Military Commands, it was a unit of razor-sharp discipline. But once the campaign to march north fell through and the force lost its purpose, discipline went slack, and by the late Joseon era even its weapons had grown so worn that it could hardly be called an army at all. From this came the phrase eoyeong-biyeong (御營非營), meaning "the Eoyeong garrison is no garrison" — and that, the popular account goes, softened into eoyeongbuyeong, a word for working in a limp, listless way. That said, the sound shift from biyeong to buyeong has never been firmly established by scholars, so it makes for a plausible story but not a settled one. It is equally possible that the mimetic word came first and the Chinese characters were fitted to it afterward.