go_dores,
You can edit the Custom Dictionary in Yosemite by opening the LocalDictionary file in Finder and then editing it. In your case by removing the accidentally added words. To find the Custom Dictionary go to the following location:
Macintosh HD > Users > Your User Name ( Example westongallagher ) > Library ( Hidden Folder ) > Spelling >
**Helpful Tip** Quick way to get to your User's Library folder is whilst in the Finder App > press and hold the ( Option ) key > select Go ( Menubar ) > Library > Then open the Spelling folder
Open the file ( LocalDictionary ) in text edit. If you haven't changed your default applications you can just double click the file and it will automatically open in Textedit. > remove the wrongfully added words > Save
After you edit the file and save it you need to restart a service called AppleSpell. You can do this multiple ways but I will give you two options.
First Option: Restart your Mac
Second Option: Launch Terminal > type in the following command:
killall AppleSpell
If you use the second option you might also have to restart the Applications that have the words displayed. And in my case I had to select the word then deselect them in order for it to underline it as misspelled again.
Please note that if you want to add words to the list they have to be in Alphabetical order. See Supporting Article below for more info.
Hope that helps,
westongallagher
Supporting Articles,
http://computers.tutsplus.com/tutorials/quick-tip-bulk-add-words-to-your-macs-sp ell-check-dictionary--mac-60820