premise:  The answer has nothing to do with their cause , however , but with the simple fact that dictionaries are mot exercises in bi - unique substitutability ; in other words , if one of the senses of run is ` operate ' ( as in She runs an engine factory ), that does mot make it valid to assume that one can substitute operate for run in We run in the marathon every year. Although recognizing this as a shortcoming of dictionaries and assigning it arbitrarily to what , for lack of a better term , we might call the genius of the language , might seem trivial to the casual observer , it is a valid matter for concern in the realm of lexicology.
hypothesis: Dictionaries are indeed exercises in bi-unique substitutability.