Definition of "vertue"

The use of this figure is great, and often necessarie and needfull to be used, the vertue and power whereof is worthie of high praise and commendation, for when commanding cannot force, nor promises allure, nor commination terrifie, as alone by themselves working in their single strengthes: yet Adhortation having al these conjoyned with it, and also sundry reasons of mightie power, as helping hands to force and move the mind forward, to a willing consent, doth prevaile in his purpose.

1577, Henry Peacham, The Garden of Eloquence