also: せいせい
noun
saving the world; promoting national welfare
Literary or formal term for benevolent governance or humanitarian efforts aimed at relieving suffering and improving society. Often used in historical or idealistic contexts.
彼は済世の志を抱いて政治家になった。
He became a politician with the aspiration of saving the world.
済世の精神は、この慈善団体の基本理念です。
The spirit of promoting national welfare is the fundamental principle of this charity.
救世 (きゅうせい) also means 'saving the world' but is more common and often used in religious or mythological contexts (e.g., 救世主 'savior'). 済世 is more about practical governance and welfare.
Compound of 済 (to relieve, to help) and 世 (world, society). The exact historical derivation is uncertain; it is a Sino-Japanese word (kango) used in classical and formal writing.