The term "most phthisic" refers to a state of extreme thinness or emaciation, often caused by a chronic illness such as tuberculosis. Some synonyms for this term include "gaunt," "scrawny," "emaciated," "skeletal," "haggard," "thin as a rail," "wasted," and "skin and bones." These words all convey a sense of extreme thinness and frailty, often associated with illness or malnourishment. While the term "most phthisic" may not be in common usage today, its synonyms are still used to describe a person or animal that appears noticeably underweight or undernourished.