The Greeks had a word for it, at least classical Greeks like Plato did. Translating the idea into English, however, has always posed a difficulty, since we don’t have one word that summarises his ideal of excellence of character and soundness of mind combined in one well-balanced individual. He defined it as “the agreement of the passions that Reason should rule”.
Sophrosyne is usually translated as temperance, moderation, prudence, self-control, or self-restraint. The idea of this harmonious balance is the basis of two famous Greek sayings: “nothing in excess” and “know thyself” — it’s the exact opposite of arrogant self-assertion or hubris.
The word has only appeared in English within the past sixty years (W H Auden used it in 1944) but it has resonated with some moderns because the idea is quite close to that of wholeness. Note the word has four syllables, not three. It derives from Greek sophron, of sound mind, prudent.