Attested in the
《周礼》 for the cesspit / drainage-pool sense, and in the
《汉书·礼乐志》 —
兴文匽武 ('promote letters, lay arms aside') — where Yan Shigu glosses
匽 as a variant of
偃 ('cease, lay flat'). The character was always rare and is replaced today by
偃 or
隐.