The noun restraint means a rule or a condition that limits or restricts someone or something. It also means a calm, controlled, and unemotional behaviour.
Synonyms are caution, control, moderation, or self-discipline.
The word origins from Old French (early 15th century) restreinte, noun use of fem. past participle of restraindre meaning “hold back”. Its sense of “reserve” is from the 16th century.
She sat there silently, sensing his restraint break.
She acts more restraint than I had expected.
The new law was about restraints on using phones during class.