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. 他參加了駐華領事館的工作，主要是因為這是為數不多的幾個空缺職位之一。