constraint
/kənˈstreɪnt; kən`strent/ n
1 [U] con-straining or being constrained 约束; 强制
act under constraint, ie because one is forced to do so 受逼迫而行动.
2 [C] ~ (on sth) thing that limits or restricts 限制性或约束性的事物
There are no constraints on your choice of subject for the essay, ie You can choose whatever subject you like. 文章内容不拘, 你可任选.
3 [U] (fml 文) strained manner; unwillingness to be friendly; uneasiness 不自然的态度; 假情假意; 拘束感
I was aware of a certain constraint on their part when they were in my presence. 我觉察到我在时他们有些拘束.