AP Stylebook editors refer to the following resources to help guide style decisions. If you do not find your answer in the Stylebook, try checking one of these other sources. You can buy them for yourself using the links below.
First reference for spelling, style, usage and foreign geographic names:
Merriam-Webster
Other references for spelling, style, usage and foreign geographic names:
American Heritage Dictionary of the English Language, Fifth Edition
Concise Oxford English Dictionary: Main edition 12th edition by Oxford Dictionaries (2011) Hardcover
Webster's Third New International Dictionary of the English Language
National Geographic Atlas of the World, Tenth Edition
The Elements of Style, Fourth Edition
The Chicago Manual of Style, 17th Edition
For aircraft names:
IHS Jane's All the World's Aircraft 2014-2015: Development & Production
For military ships:
Jane's Fighting Ships 2016/2017: Yearbook
For nonmilitary ships:
LLOYDS REGISTER OF SHIPS 1989-90 (3 VOLS A-G/H-O/P-Z)
For railroads:
The Official Railway Guide: Freight Service Edition,The Bulk Connection March/April 1990
For federal government questions:
Congress At Your Fingertips 115th Congress 1st Session 2017
For non-U.S. government questions:
Political Handbook of the World
For religion questions:
Handbook of Denominations in the United States 13th Edition
Other references and writing guides consulted in the preparation of the AP Stylebook:
More Language That Needs Watching
THE WORD: An Associated Press Guide To Good News Writing
Modern American Usage: A Guide
A Dictionary of Modern English Usage, Second Edition
Fowler's Dictionary of Modern English Usage
Harper Dictionary of Contemporary Usage