from The Century Dictionary.
- Acting within or upon itself; loosely, reciprocally active.
Sorry, no etymologies found.
But 'tis pure fire -- and they mere matter are; it has THEM, not they IT: and so I choose, for man, that a third thing shall stand apart from both, a quality arise within the soul, which, intro-active, made to supervise and feel the force it has, may view itself and so be happy. "
An Introduction to the Study of Robert Browning's Poetry Hiram Corson 1869