Introduction to a book (7)
I believe the answer is:
preface
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">introduction to a book</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for preface that I've seen before include "Preamble" , "Opening words" , "Introductory text" , "Book's introduction" , "Foreword" .)