Adjective
jesty (comparative more jesty, superlative most jesty)
Inclined to jest; waggish; sportive.
Although Jesty may have been the first to discover it, Jenner made vaccination widely accessible and has therefore been credited for its invention. Source: Internet
In the years following 1770, at least five investigators in England and Germany (Sevel, Jensen, Jesty 1774, Rendell, Plett 1791) successfully tested a cowpox vaccine in humans against smallpox. Source: Internet