For spelling follow manual entries or use the first spelling listed in:

             Merriam-Webster’s Collegiate Dictionary
                        (11th edition, reprinted with some changes annually)
            Merriam-Webster Unabridged (prepaid for internal use)
            Webster’s Third New International Dictionary

Other general dictionaries include:

The American Heritage Dictionary of the English Language
Webster’s New World College Dictionary
Random House Webster’s College Dictionary
Oxford English Dictionary
(prepaid for internal use)

Specialized dictionaries:

Oxford Bilingual Dictionaries (prepaid for internal use)
Dictionary of American Regional English
The New Hacker’s Dictionary

The Oxford Dictionary for Scientific Writers and Editors
Random House Historical Dictionary of American Slang
Webster’s Geographical Dictionary
Webster’s New Biographical Dictionary

Style and Grammar

Standard and useful references include:

The American Heritage Book of English Usage
The Chicago Manual of Style
(prepaid for internal use)
The New York Public Library Writer’s Guide to Style and Usage
Webster’s Dictionary of English Usage
Wired Style Principles of English Usage in the Digital Age
Words Into Type