You may recall one or two of your elementary teachers advising you to spell a word the way you would say it. While that didn’t work for knight, it does work for nonetheless.
Because this adverb is really a collection of three words, many writers like to spell it as such with a space between each syllable. However, we actually speak the three words as if it were one, typically cutting a tic out of our pause between words in a sentence. So, nonetheless is the correct spelling.
In addition, when punctuating, a comma always goes after nonetheless. To wit: Nonetheless, Los Angeles is taking steps to become more cultural with the addition of new museums. If nonetheless appears in the middle of a sentence, the word is set off with commas on both sides of it, as in: The mayor of New York City, nonetheless, maintains that no American city can match his for cultural attractions.
My name is Rob Bignell. I’m an affordable, professional editor who runs Inventing Reality Editing Service, which meets the manuscript needs of writers both new and published. I also offer a variety of self-publishing services. During the past decade, I’ve helped more than 300 novelists and nonfiction authors obtain their publishing dreams at reasonable prices. I’m also the author of the 7 Minutes a Day… writing guidebooks, four nonfiction hiking guidebook series, and the literary novel Windmill. Several of my short stories in the literary and science fiction genres also have been published.