chiefly
adv. 主要地；首先
例句
He's travelled widely, chiefly in Africa and Asia.
他游历了许多地方，主要在非洲和亚洲。
《牛津词典》
We are chiefly concerned with improving educational standards.
我们主要关心的是提高教育水平。
He joined the consular service in China, chiefly because this was one of the few job vacancies.
他参加了驻华领事馆的工作，主要是因为这是为数不多的几个空缺职位之一。
《柯林斯英汉双解大词典》
