Noun, する verb, and の adjective
きんえん
ここが禁煙スペースだってこと、忘れてるわけないじゃない。
How could I forget that this is a no smoking area?
毎週月曜日は禁煙の日って決めているんです。
I've decided to make every Monday a no smoking day.
母親に禁煙するように言ったんですが、逆に母親から、禁煙したらおそらく気が狂って、父親と離婚することになると言われました。
I told my mom to quit smoking and she told me that if she did, she would probably go crazy and my parents would get divorced.
If smoke is prohibited you probably shouldn't smoke. Aka no smoking, okay?
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.