This book is about people compiling dictionaries for others. The “大渡海(だいとかい)” is the name of the dictionary being created in this book, named thus because it will be “a ship to enable all people to voyage freely across the sea of words”.
「きみの力を、大渡海に注いでほしい」 I want you to give all you’ve got to Daitokai!
「そこに美と喜びを見いだす馬締は、やはり辞書づくりに向いている」 Majime’s perception of beauty and joy in that process marked him beyond all doubt as a born lexicographer.