How can I tell OS X to flag a name as being misspelled? I have a co-worked whose name is Jennett. In Pages, I added her to my local dictionary (located at ~/Library/Spelling/LocalDictionary) by right-clicking on her name and choosing Learn Spelling.

However, OS X is not flagging Jennet with one "t" as being misspelled. 

How can I make Jennet with one "t" be flagged as being misspelled?

I assume this problem stems from the fact that jennet—a female donkey—is found in the OS X dictionary. However, given that I don't write much about donkeys, let alone female donkeys, I'd prefer to be notified when I'm misspelling a co-workers name.
Removing words from the built-in dictionary is apparently more difficult than I thought it would be. Since your question is about how to prevent a particular misspelling of your co-worker's name, I have an alternate solution.

You can add "Jennet" to Mac OS X's text substitution list in System Preferences -&gt; Language &amp; Text -&gt; Text



It will automatically correct the spelling for you each time you misspell it. You could add other variant misspellings for completeness, like "Jenet" or even make it auto-capitalize "jennett", but since most other misspelling variants don't have obscure English homonyms these will show up as misspellings.