The origin of the Japanese word keizai (経済 'economy'')

No you won't see this yojijukugo in common use, but it is a widely accepted etymology of a very common word 経済, economy.

When Japan opened to the rest of the world in mid-19th century, it had to learn to communicate a lot of new things. Despite the thousands years of both inherited Chinese and indigenous Japanese scholarship, Japanese at the time lacked words to convey many concepts. Names for new objects as well as for abstract ideas had to be invented. In those days, the Japanese did not rely as much on katakanese, so they put their minds to make up new kanji-based words. Most of times,  those would  be very clever renderings of the meanings deciphered from European words and then reassembled  in Japanese. For example, the word for society, shakai, would be made of two characters 社会　meaning "gathering in/around a Shinto shrine", which rather neatly and with a hint of metonymy gets across what a contemporary Japanese would envision society like. Swap the characters, and here comes 会社 kaisha, "company" or "firm" (by the way, both société in French).

Economy in the sense of a discrete domain, (egregiously) thought to exist independently of everything else, such as society, environment, or psychology, is a relatively new way of thinking about the relations between money, commodities and labour. It was novel to the 19th century Japan (and, granted, just barely established in the West too). Understandably, there was no corresponding Japanese word for it. So Meiji intellectuals, well versed in Classical Chinese, digged out a wise maxim 經世濟民 keisei-saimin from The Book of The Master Who Embraces Simplicity, a 4th-century treatise by Ge Hong, a Jin Dynasty official.

The meaning of  the phrase can be interpreted  as "keeping the world in order will help out the people". This idea shows a strong influence of the Chinese political concept of  the Mandate of Heaven with its insistence that "moral government brings peace to the country"). That kind of understanding echoes well with the parallel Western concept of political economy. Nearly two centuries of intellectual debate It is also rather contrary to the latter-day Neo-Classical idea of economy as a self-contained and self-serving Moloch, to the quantified attributes of which (such as growth, controlled inflation and an infinitely expanding slew of other numerical meta-entities) everything else needs to be sacrificed (aka  #GoodForTheEconomyShitForThePeople). It is interesting to see how economy from a way of social advancement through economic means  has come to mean the opposite, the advancement of economic factors  at the expense of social "externalities".