This is the 16149th most frequent Korean word.
불만으로
"불만으로" means "discontentedly" or "with dissatisfaction" in English.
In this sentence, '불만으로' indicates the reason for his action, showing discontent as a cause for resignation.
그는 회사의 결정에 불만으로 사직서를 제출했다.
He submitted his resignation due to dissatisfaction with the company's decision.
Here, '불만으로' is used to attribute the dissatisfaction that inspired her writing the complaint-filled letter.
그녀는 친구의 불성실한 태도에 대해 불만으로 가득 찬 편지를 썼다.
She wrote a letter full of complaints about her friend's insincere attitude.
In this case, '불만으로' explains the dissatisfaction as the driving force behind the protests.