noun, な adjective
You're cool and quiet. That's you, daddio. Nice and cool-headed and calm. So much composure
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.
I tried to keep my tone as calm as possible.
Staying calm is very beneficial.
You need to learn how to be cool-headed when handling internet trolls.