Auctoritas is a Latin word and is the origin of English "authority". While historically its use in English was restricted to discussions of the political history of Rome, the beginning of phenomenological philosophy in the 20th century expanded the use of the word.
In ancient Rome, Auctoritas referred to the general level of prestige a person had in Roman society, and, as a consequence, his clout, influence, and ability to rally support around his will. Auctoritas was not merely political, however; it had a numinous content and symbolized the mysterious "power of command" of heroic Roman figures.
Noble women could also achieve a degree of Auctoritas. For example, the wives, sisters, and mothers of the Julio-Claudians had immense influence on society, the masses, and the political apparatus. Their Auctoritas was exercised less overtly than their male counterparts due to Roman societal norms, but they were powerful nonetheless.
According to French linguist Emile Benveniste, auctor (which also gives us English "author") is derived from Latin augeō ("to augment"). The auctor is "is qui auget", the one who augments the act or the juridical situation of another.
Auctor in the sense of "author", comes from auctor as founder or, one might say, "planter-cultivator". Similarly, auctoritas refers to rightful ownership, based on one's having "produced" or homesteaded the article of property in question - more in the sense of "sponsored" or "acquired" than "manufactured". This auctoritas would, for example, persist through an usucapio of ill-gotten or abandoned property.
Politically, auctoritas was connected to the Roman Senate's authority (auctoritas patrum), not to be confused with potestas or imperium (power), which were held by the magistrates or the people. In this context, Auctoritas could be defined as the juridical power to authorize some other act.