What does the word propriety mean in the context?

Question

Though the law of England, on the subject of the press, is as servile to this day as it was in the time of the Tudors, there is little danger of its being actually put in force against political discussion, except during some temporary panic, when fear of insurrection drives ministers and judges from their propriety; and, speaking generally, it is not, in constitutional countries, to be apprehended, that the government, whether completely responsible to the people or not, will often attempt to control the expression of opinion, except when in doing so it makes itself the organ of the general intolerance of the public.
(source: On Liberty By John Stuart Mill)

What does the bolded word "propriety" mean? I did look it up but could not figure out the meaning for the context. For me, neither being appropriate or conformity sounds right.

Could you help me clarify it?

Answer 1

The meaning is similar to "appropriate", but it also connotes noble or "gentlemanly" behavior of the type that is stereotypical of the Victorian era, the era in which On Liberty was written.

In this context, "the propriety of the judges and ministers" refers to the gentlemanly behavior of not getting what one wants through force, force of law or otherwise. The author gives "the fear of insurrection" as an exception, allowing them to take a break from gentleness for the sake of averting public panic.

Answer 2

"Appropriate" isn't right only because it is an adjective and "propriety" is a noun. It does mean appropriateness or conforming to acceptable behavior. The root of both propriety and appropriate is "proper." The sense is that fear of insurrection sometimes drives ministers and judges to behave improperly.

https://www.etymonline.com/word/propriety