Restrained is a past participle verb which means held back. Thus it can be used in the following possible sentences:
I wanted to eat a second doughnut, but restrained myself.
The drunk man had to be restrained because he was getting violent.
When in a car, it is best to wear a seatbelt so you are restrained if the car crashes.
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The rescued fighting dog had to be restrained, when it was
around other dogs.
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Restrained elegance seems to have something to do with bondage
and BDSM. There is an adult website called "Restrained Elegance"
which has pictures and videos of women in barefoot bondage.
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Yes, it can be, to mean either subdued (restrained laughter) or physically secured (a restrained prisoner). It is the past tense and past participle of the verb to restrain, so is otherwise a verb form.