From Longman Dictionary of Contemporary Englishmainmain1 /meɪn/ ●●●S1W1 adjective [only before noun]1MAINlarger or more important than all other things, ideas etc of the same kindThe main reason for living in Spain is the weather.What do you consider to be the main problem?Our main concern is that the children are safe.a summary of the main points of the agreementthe main aim of the meetingI’ll meet you outside the main entrance.the main bedroom► see thesaurus at important2 →the main thing → an eye for/on/to the main chanceat eye1(22)THESAURUSmain larger or more important than all the othersthe main entrance of the buildingthe main reason for his decisionchief/principal most important. Chief and principal are more formal than main, and are often used in written EnglishCoffee is the country’s principal export.What is the company’s chief objective?major very important or seriousSmoking is a major cause of heart disease.Street crime is becoming a major problem.key most important, or the one that everything or everyone else depends onEducation is likely to be a key issue in the election campaign.Hooper was a key member of the team. Diet is key. number one especially spoken most important or best – this phrasesounds a little informal and it is used especially in spoken EnglishReliability is the number one priority.the number one cause of death He is still in the number one position.primary most important – used especially about the most important aim, role, cause, or concern. Primary is more formal than mainThe primary aim of the project was to help students develop their communication skills.Security is our primary concern.The primary function of the university was considered to be the teaching of ‘the great cultural disciplines’. prime very important or most important – used especially about the most important reason, cause, or aim, or about the most likelytarget or suspect. Prime is more formal than mainTheir prime objective is to increase profits for their shareholders.Tourists are prime targets for theft and robbery. core most important – used especially about the things that people should pay most attention tothe core skills of reading and writingHe wants the company to focus on its core business – advertising.The party’s core values are individual freedom and reducing the amount of government bureaucracy.central most important and having more influence than anything elseThe U.S. played a central role in the peace negotiations.a central theme of the bookThe central question is, why are people still so attached to their cars?predominant most common, typical, or importantYellow was the predominant colour everywhere. High arched windows are a predominant feature in English churches.New York still has a predominant role in the contemporary art world.