Antonyms for the word "most infective" include words such as "least contagious," "least infectious," and "least virulent." These words denote a low or limited capacity of an infectious agent, such as a virus, bacterium or parasite, to spread or cause disease. Other antonyms include terms such as "inert," "non-infectious," or "harmless," which suggest that the substance or organism in question does not pose a threat to human health or wellbeing. These contrasting words are important to grasp in understanding the degree of risk and potential danger posed by various infectious agents, and can help individuals make informed decisions about how to protect themselves and others from disease.