The headword is a nominative masculine/feminine singular adjective composed from xai/rw ("rejoice") and kako/s ("bad"). This form is equivalent in meaning with the more frequent e)pixaire/kakos.
The concept of taking delight in other's misfortune is best-known nowadays by the German word Schadenfreude. The English epicaricacy (a transliteration of the Greek e)pixairekaki/a) is obscure at best.
See also epsilon 2767 and eta 97.