興じる
きょうじる · kyoujiru · JLPT N1 · noun
to amuse oneself
🎈 興 (kyō) = excitement/interest + じる verb ending: to let fun rise up and enjoy oneself
The kanji 興 means excitement or interest, as in 興奮 (kōfun, excitement). Adding じる makes it a verb: to get excited and enjoy oneself, to make merry.