potestas

Potestas, potestatis, f., is third declension, formed on possum. Two strands run through it. The legal and political one: a magistrate holds potestas, and patria potestas is the father lifelong authority over his household, one of the strangest things in Roman law. The everyday one: potestas plus a gerund in the genitive means simply "the chance to do something" - potestas loquendi, the opportunity to speak.

Roman lawyers keep it apart from its neighbours. Imperium is military command with the power of life and death; auctoritas is influence with no legal handle at all, the Senate specialty. And note the construction: potestas faciendi, never potestas facere.