Entry 1 sense Webster, 1913 Poisonous /poiz'-ən-əs/ · Poi·son·ous · IPA /ˈpɔɪzənəs/ 01 a. Having the qualities or effects of poison; venomous; baneful; corrupting; noxious. 1. Having the qualities or effects of poison; venomous; baneful; corrupting; noxious.