Emily Dickinson Lexicon

POI-SON, n. [poiz'n; Fr. poison; Arm. empoesoun, pouison; Sp. ponzoña; Port. peçonha. Qu. its alliance to L. pus. See Class Bs, No. 25.]

1. Any agent capable of producing a morbid, noxious, or dangerous effect upon any thing endowed with life. All medicines possessing sufficient activity to be of much value, are always poisons in inordinate or excessive quantities; and every thing poisonous is capable of proving medicinal in suitably reduced quantities. The ancient Greeks employed the same word, both for a medicine and a poison. There are as many different modes in which poisons operate as there are different and distinct medicinal powers of any material activity. According to the popular notion, those articles only are poisonous, which are capable of producing morbid, noxious, or dangerous effects, in comparatively small quantities; but there is no just foundation for such a distinction.
2. Any thing infectious or malignant; as, the poison of pestilential diseases.
3. That which taints or destroys moral purity or health; as, the poison of evil example; the poison of sin. – South.