Which term is used to describe harmful or poisonous substances affecting health?

The term "nocuous" is accurately used to describe harmful or poisonous substances that can negatively affect health. This word originates from the Latin "nocuus," meaning "harmful" or "injurious." In medical contexts, nocuous agents refer to toxins or hazardous materials that can cause disease or adverse health effects when an individual is exposed to them.

The other terms do not convey this meaning. "Numiform" relates to something that is shaped like a coin and does not pertain to health or harmful substances. "Nullipara" refers to a woman who has never given birth, which again is unrelated to harmful substances. "Nidus" indicates a nest or a place where something can develop, often used in medical terminology to describe a focus of infection, but it does not specifically denote harmful substances affecting health. Thus, "nocuous" is the most appropriate term in the context of harmful or toxic impacts on health.