ˈthumb ˌindex BrE AmE noun [countable]
a line of round cuts in the edge of a large book which have the letters of the alphabet on them and help you find the part of the book you want
ˈthumb ˌindex BrE AmE noun [countable]
a line of round cuts in the edge of a large book which have the letters of the alphabet on them and help you find the part of the book you want
Longman Dictionary of Contemporary English. Longman - Словарь современного английского языка. 2012