The phrase "most mensurable" refers to something that is measurable to the greatest extent. The antonyms for this phrase would be something that is not easily measurable or cannot be easily quantified. Some antonyms that come to mind include immeasurable, intangible, intangible, intangible, inaccessible, or elusive. These words indicate a quality or characteristic that is difficult to quantify, and cannot be easily counted or measured. For example- love, happiness, honesty, beauty, peace - these qualities are not easily measurable using a standard unit of measurement like length, weight, or time. They more require qualitative evaluation and subjective interpretation.