百年河清 ひゃくねんかせい Meanings Expression waiting for one hundred years for the waters of the Yellow River to clear; waiting in vain for an unlikely event; waiting for pigs to fly; when the sky falls, we shall catch larks Kanji 百 hundred. Read as ヒャク. 年 year. Read as ネン. 河 river 清 clean. Read as セイ. Word lists Yojijukugo (四字熟語) Jinuma: Japanese Dictionary · Word lists