mainly synonym chiefly The book is aimed principally at beginners. No new power stations have been built, principally because of the cost.Extra examples Change management is principally concerned with people, their attitudes and skills. The farms are principally arable. The measures were principally designed to tackle the problem of homelessness. The sportswear range is aimed principally at the skiing market. The tax was very unpopular, principally because it hit the poor hardest.