The term "most tractile" carries the meaning of being easily shaped or molded. Antonyms of this word include "rigid," "inflexible," and "unyielding." If someone or something is described as "rigid," it means that they are stiff and difficult to bend or shape. Similarly, if something is "inflexible," it means that it cannot be easily altered or changed. Whereas, if something is "unyielding," it means that it is firm and hard to change. Therefore, if a person wants to express the opposite of "most tractile," they can use these antonyms to describe the characteristic they wish to convey.