朽 means 'decay'

This collection may seem bleak. The essays spotlight withering plants, rotting trees, and entire nations in decline. The bundle focuses on losing physical abilities and dying of old age. And the 萎 essay touches on dampened hopes and sagging spirits. But the most-common 朽 word characterizes artworks as enduring. And 枯 can mean "to mature," applying to both people and technology. As that essay shows, the Japanese have an odd affection for dead trees, also using 枯 in fun proverbs. Finally, the study of 衰 reflects that yes, decline occurs, but so does prosperity; vicissitudes are inevitable parts of life.