High Speed
Express
noun, な adjective, の adjective
It's pleasant but also fast. When getting on a train, it's nice to find a train that's both of these things. What makes it pleasant? That would be the high speed. What makes it fast? Also the high speed. Really, if you're on a train you'd rather get to your destination sooner than later, so a high speed 快速 train is the way to go.
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.
コウイチは、昨晩、150キロの快速球を投げ込んで才能の違いを見せつけている夢を見た。
Koichi dreamt last night that he showed off his talent of throwing with a 150-kilometer-per-hour fastball.