Sentence:  We had now reach'd the closest point of union; but when he backened to come on the fiercer, as if I had been actuated by a fear of losing him, in the height of my fury I twisted my legs round his naked loins, the flesh of which, so firm, so <WSD>springy</WSD> to the touch, quiver'd again under the pressure 
Meaning of the word marked with <WSD> tags:  That returns rapidly to its original form (as a spring does) after being bent, compressed, stretched, etc.