Mortality Subjection to death. It is a term also used to signify a contagious disease which destroys great numbers of either men or beasts. Bills of Mortality are accounts or registers specifying the numbers born, married, and buried, in any parish, town, or district. In general, they contain only these numbers, and even when thus limited are of great use, by showing the degrees of healthiness and prolifickness, and the progress of population in the place where they are kept.