I'm currently trying to figure out the exact meaning of the word duress in the sense forcible restraint or imprisonment. The Oxford Dictionary tells me that this meaning of the word is archaic. I've been searching for examples on Google Books for a while and have found, among others, this sentence:
It is not always necessary that a person be actually confined within the silent walls of a jail or prison to be under duress, restraint, or imprisonment.
My question is: what is the special meaning here that sets duress apart from restraint and especially imprisonment so it is listed here together with the two other words?