THE 1977 YAPESE-ENGLISH DICTIONARY written by John Thayer Jensen with the assistance of John Baptist Iou, Raphael Defeg, and Leo David Pugram.
Please note that the 1977 Yapese Reference Grammar is available here.
A larger more browsable Yapese dictionary is available at trussel.
Although tekinged.com is dedicated to the Palauan language, it is happy to provide this book as well due to the close ties within Austronesian languages.