Onyomi Examples
究竟 （クッキョウ） after all, in the end, finally, excellent, superb, handy, appropriate, ideal, robust, brawny, muscular, strong, sturdy
究竟 （クキョウ） culmination, conclusion
Kunyomi Examples
終わる （おわる） to end, to come to an end, to close, to finish
遂に （ついに） finally, at last, in the end, after all, never (happened)