Wiktionary
n. (cx historical Ancient Rome English) An interregnum after the death of an emperor.
Wikipedia
Justitium is a concept of Roman law, equivalent to the declaration of the state of emergency. It was usually declared following a sovereign's death, during the troubled period of interregnum, but also in case of invasions. However, in this last case, it was not as much the physical danger of invasion that justified the instauration of a state of exception, as the consequences that the news of the invasion had in Rome - for example, justitium was proclaimed at the news of Hannibal's attacks.
According to Giorgio Agamben, justitium progressively came to mean, after the Roman Republic, the public mourning of the sovereign: a sort of privatization or diversion of the danger threatening the polis, as the sovereign claimed for himself the auctoritas, or authority, necessary to the rule of law.
Usage examples of "justitium".
To prevent the Tribune from putting these rogations to the vote, the Consuls declared a justitium, during which no business could be legally transacted.
Quintius to the city put a termination to the justitium, which lasted only four days.