The word "most exertive" suggests a high level of effort or activity. Its antonyms - words that denote the opposite meaning - include "least exertive," "easy," "effortless," "idle," "passive," "relaxing," and "restful." These words describe situations or activities that require little or no energy, physical or mental exertion, or exertion of force. Alternatively, the word could be replaced by phrases such as "least strenuous," "least demanding," or "least challenging." The antonyms of "most exertive" can be used to convey a sense of relaxation, leisure, or calmness, which are the opposite of the high-energy, intense, and active nature of the original term.