Pes′ti‐len″tial (?), a. [Cf. F. pestilentiel.] 1. Having the nature or qualities of a pestilence. “Sends the pestilential vapors.” Longfellow.
2. Hence: Mischievous; noxious; pernicious; morally destructive.
So pestilential, so infectious a thing is sin. Jer. Taylor.