simple
"Simple" is a very common and useful English word. It works mainly as an adjective, but it also has a noun sense used in older or specialized contexts. Here are the most important meanings you'll encounter.
In older English, a 'simple' was a plant used as medicine on its own, without being mixed with other ingredients. You are unlikely to hear this in everyday conversation today, but you might come across it in historical texts or books about herbal medicine.
historical, herbal medicine · Formal, more common in older texts