chiefly

1. ADV You use chiefly to indicate that a particular reason, emotion, method, or feature is the main or most important one. 首要地

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。