What did Gustave Flaubert mean by seeking le seul mot juste?

For Gustave Flaubert, the pursuit of le seul mot juste—or "the unique right word"—was a fundamental aspect of his rigorous method of composition. Flaubert believed that there was no such thing as a synonym; he argued that for every thought, there existed only one precise word capable of conveying it accurately.1

His commitment to this principle was driven by a desire to achieve a style that was as "rhythmical as verse and as precise as the language of science". By tracking down the exact word, he aimed to ensure that language adhered as closely as possible to his underlying thought, creating a beautiful and penetrating effect.1

Beyond mere precision, Flaubert sought a harmony of sounding syllables in his prose, intending for his writing to appeal to a reader's subconscious mind much like music does. This relentless search for perfection made the act of composition a source of great "anguish" for the author, as he would rewrite his work constantly to achieve the desired balance of cadence and exactitude.123