They tried to keep it quiet but, somehow, half the village knew about the news in a few days.

keep 在这里是动词，意思是"保持、维持"某种状态。 quiet 是形容词，意思是"安静的、不声张的"，在这里指"不对外公开"的状态。 keep quiet 是一个固定短语，意思是"保持沉默、保守秘密"，指不把某事告诉他人。