germ

Usage You've heard it many times. Some food falls on the floor, and someone (usually an adult) says, "Don't eat that now. It has germs on it." The word germ has been used to refer to invisible agents of disease since the 19th century, when scientists were first learning about the nature of disease. Similarly, the term microbe, which comes from the Greek prefix mikro-, "small," and word bios, "life," is a term that arose in the late 19th century in reference to the microscopic organisms that caused disease. The terms germ and microbe thus became associated with an early era of scientific research in which knowledge was very limited, and they are no longer used much by scientists. Thanks to generations of research, scientists today can usually identify the specific agents of disease, such as individual species of bacteria or viruses. When they want to refer generally to agents of disease, they use the term pathogen, which comes from Greek pathos, "suffering," and the suffix -gen, "producer." The term microorganism is used to refer to any one-celled microscopic organism, whether it causes disease or is harmless.