Did Claude Debussy come up with the term impressionism and applied it to his music?
No; A critic saw a painting (Impression: Sunrise) by Claude Monet at an exhibition in Paris in 1874. He didn't like it, and mockingly called the show "exhibition of the impressionists". Claude Debussy's music evoked a similar fleeting mood and misty atmosphere, which is why the connection was made between the two. Although the derisive implication was eventually lost, the term impressionist stuck.