First Class, Top Notch, Top Grade
noun, の adjective
This is a weird one. You have one stream. This is first rate stream material we have here, though. If you think about it, if you only have one stream (instead of a ton of streams), you can put all your effort and energy into it. When you do that, you're making sure it is a first rate stream in terms of quality and anything else.
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.
That's something only first-rate pianists can do.
My sister fell in love with a wealthy, first-class gentleman.
Koichi is now a member of the upper class. He will meet a bunch of celebrities and start going to champagne parties soon.