The phrase "most instituting" can be synonymous with "most establishing," "most initiating," or even "most implementing." All of these terms have a similar connotation of setting something in motion or putting something into effect. Other synonyms for "most instituting" could include "most inaugurating," "most commencing," or "most commencing." When searching for the right word to use in a given context, it's important to choose one that accurately captures the intended meaning and tone. Different synonyms may be more appropriate depending on the situation or the style of writing required.