Self Discipline, Self Restraint
Noun and する verb
じしゅく
役員の不祥事発覚を受け、本日は全社員が営業活動を自粛致します。
With the staff scandal coming to light, all employees are to restrain themselves from doing business activities today.
If you're solemn by yourself, you have a lot of self control. You don't need anyone to tell you to be that way, you have your own self discipline.
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.