Meaning of MOSTLY in English

Frequency: The word is one of the 3000 most common words in English.

You use ~ to indicate that a statement is generally true, for example true about the majority of a group of things or people, true most of the time, or true in most respects.

I am working with ~ highly motivated people...

Cars are ~ metal. and women, ~ in their 30s...

= mainly

ADV: ADV with cl/group

Collins COBUILD.      Толковый словарь английского языка для изучающих язык Коллинз COBUILD (международная база данных языков Бирмингемского университета) .