Someone who is ~ continues trying to do something difficult rather than giving up quickly. (FORMAL)
ADJ
Someone who is ~ continues trying to do something difficult rather than giving up quickly. (FORMAL)
ADJ
Collins COBUILD. Толковый словарь английского языка для изучающих язык Коллинз COBUILD (международная база данных языков Бирмингемского университета) . 2012