‘The word “power” (pouvoir) is vague in French.’ Thus Georges Duby, writing in 1991 about women and power. Although he proceeded in this context to provide a precise definition of power, his comment is perhaps more significant than even Duby realized. For while Duby intended merely to set the stage for his subsequent analysis, he inadvertently touched upon a central fact that describes many of the dozens of books and articles written over the past twenty years employing the word ‘power’ either in their titles or, more rarely, in their methodological apparatus. While studies of power, then, are ubiquitous, what an author means by power is often less well articulated, even vague. Of course any sort of lexical imprecision, or, perhaps, lexical malleability, serves a double function in the contexts both of everyday communication and of the writing of history. The very ubiquity of a word or concept like power as a tool for historical analysis renders it at once powerless, because of its semantic vagueness, and powerful, because each reader is capable of infusing it with meaning on an individual, and highly subjective, basis. That is to say that imprecision lends potency to a concept, for the meaning that is lacking in the word itself can be and is supplied in every context by those who hear, read, or experience the concept in question. Given this fact, it is perhaps not surprising that historians have only hesitantly ventured to define power with precision; the limitations of any such definition would serve to localize and, to a degree, minimize the efficacy of power as a concept. That Duby chose in 1991 to define power rather precisely as the range of meanings ‘expressed by the Latin term potestas …, that is, the power to command and punish’, is thus somewhat surprising, and not a little disappointing. For one thing, by limiting power conceptually to the ability to command and punish, Duby closed off other potential ways of thinking about power, ways that might have led him to conclude differently about the capacity of women to exercise power. Furthermore, the real question is whether the words for power were vague in medieval Latin, not in modern French, or, at least, whether specific authors writing in medieval Latin also found power to be a vague concept.