chief·ly 
/ˈtʃi:fli/ adverb
/ˈtʃi:fli/ adverb : mainly or mostly — used to identify the most important part of something, reason for something, etc. ▪ We're chiefly concerned with protecting the environment. ▪ His greatest works—chiefly those written between 1640 and 1685—are still read today. ▪ an animal that hunts chiefly by smell ▪ The disease occurs chiefly in children. ▪ The rock is composed chiefly of quartz.
