Definition of leader noun from the Oxford Advanced Learner's Dictionary
leader
noun
ˈliːdə(r) ˈliːdər
1a person who leads a group of people, especially the head of a country, an organization, etca political/spiritual, etc. leaderthe leader of the partyunion leadersHe was not a natural leader.She's a born leader.2a person or thing that is the best, or in first place in a race, business, etcShe was among the leaders of the race from the start.The company is a world leader in electrical goods. see also market leader3(British English) (alsoconcertmasterNorth American English, British English)the most important violin player in an orchestra4(British English) = editorial
ˈliːdə(r) 
ˈliːdər 
1 a person who leads a group of people, especially the head of a country, an organization, etca political/spiritual, etc. leaderthe leader of the partyunion leadersHe was not a natural leader.She's a born leader.