Quick, Fast, Rapid, Swift
noun, な adjective
Things that are swift and fast are going to be quick and fast and rapid and swift. So many quick things.
じんそく
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
こちらの件に関して、迅速かつ丁寧にご対応頂き誠に有り難うございます。
I appreciate your prompt and polite response to this matter.