vivacity

noun

Etymology: From vivac(ious) + -ity, borrowed from Latin vīvācitās.

1. The quality or state of being vivacious.

   “But reposed natures may do well in youth. […] On the other side, heat and vivacity in age, is an excellent composition for business.”

   “1738, David Hume, A Treatise of Human Nature, Book I, Part I, Section III. Of the Ideas of the Memory and the Imagination, We find by experience, that when any impression has been present with the mind, it again makes its appearance there as an idea; and this it may do after two different ways: either when in its new appearance it retains a considerable degree of its first vivacity, and is somewhat intermediate betwixt an impression and an idea: or when it entirely loses that vivacity, and is a perfect idea.”