The Chicago Manual of Style is the guide editors use when we copyedit manuscripts. When we have a question about whether to use a comma with an adverbial phrase or to set the name of a sculpture in italics or quotation marks or anything else, we check with this book, all 1,144 pages of the most recent (seventeenth) edition.
In section 2.54, it suggests editors use the latest edition of Merriam-Webster’s Collegiate Dictionary to check spellings. When I come across a word I’m unsure about, I pull up the online edition and type the word in the search box.
Usually, for me, I’m checking whether to delete a hyphen from a word. For instance, I may check whether it’s pre-order or preorder or human-like or humanlike. (In case you’re wondering, both do not take a hyphen.) This is an example of when spellcheck may mark a word as being spelled correctly, yet it would still need to be changed because the spelling does not align with the one in the dictionary.
Why Take the Time to Check the Dictionary?
Your editor will refer to Merriam-Webster's Collegiate Dictionary frequently during your edit. If you have taken the time to change your spellings to match the dictionary listings, your editor will likely still double-check with the dictionary, but it means they won’t have to do a find and replace over and over to fix these words. If you have a long book and/or your editor is charging hourly, this could save you some pretty sizable bucks.
What Words to Check
As I said, in my experience, the changes most often come from prefixes (like the pre in preorder) and suffixes (like the like in humanlike) and whether they take a hyphen. However, if any word sets off a question mark in your head, look it up.
To Pay or Not to Pay
I pay for an annual subscription to Merriam-Webster’s online dictionary, which offers a choice between the unabridged and the collegiate dictionaries. It also offers a thesaurus option, an encyclopedia option, and two foreign dictionaries. If you’re a word nerd, you’ll appreciate the expanded definitions and etymologies (word histories). Plus there are no ads. The cost is pretty reasonable. As of this writing, it is $29.95 for a year or $4.95 for a month. However, if you don’t feel like paying, you are usually safe with the free online version, as there is rarely a difference.