n. The state of being sportive; disposition to mirth; playfulness; mirth; gaiety; frolicsomeness: as, the sportiveness of one's humor.
WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
n. lively high-spirited playfulness
Word Usage
"At this time a slight sleep relieved me from the pain of reflection, which was disturbed by the approach of a beautiful child, who came running into the recess I had chosen, with all the sportiveness of infancy."