efficaciousness Copy link Outline 1. vis, vim, vi, f.2. virtus, ūtis, f. • efficaciousness ; efficacy 1. vis, vim, vi, f.: to perceive the e. of certain herbs, (herbarum) vim et effectum videre, Cic.: v. influence, force. 2. virtus, ūtis, f.: e. of (magic) plants, herbarum v., Ov. Phr.: to have greater, less e., plus, minus valere, Hor.: v. effectual.