The following are standard references for the AP Stylebook and for material not covered by the Stylebook.
First reference for spelling, style, usage and foreign geographic names:
Merriam-Webster
Other references for spelling, style, usage and foreign geographic names:
The American Heritage Dictionary of the English Language, Fifth Edition, Houghton Mifflin Harcourt, Boston and New York, 2011
Concise Oxford English Dictionary, Twelfth Edition, Oxford University Press, Oxford, 2011
Webster's Third New International Dictionary of the English Language, unabridged, Merriam-Webster, Springfield, Massachusetts, 1993
AP Stylebook & Merriam-Webster Online integrates descriptions from the Stylebook's primary dictionary into a single web-based resource with AP Stylebook Online. That digital database from Merriam-Webster is more up to date than any print Merriam-Webster dictionary.