From Longman Dictionary of Contemporary Englishmainlymain‧ly /ˈmeɪnli/ ●●●S2W2 adverb 🔊 🔊 MOSTused to mention the main part or cause of something, the main reason for something etc syn primarily 🔊 Her illness was caused mainly by stress. 🔊 The workforce is mainly made up of women. 🔊 I don’t go out much, mainly because I have to look after the kids. 🔊 Increased sales during the summer were mainly due to tourism. 🔊 We talked about various things – work, mainly.Grammar• You usually use mainly in the middle of a sentence: They play mainly on Sundays.People go there mainly because of the beautiful beaches.• You also use mainly at the end of a sentence, especially in conversation: I read novels, mainly.• It is much less commonly used at the beginning of a sentence.RegisterIn written English, people often prefer to use chiefly or primarily, which sound more formal than mainly:The disease is caused chiefly by poor sanitation.