In addition to the standard MainDictionary and UserDictionary dictionaries, C1SpellChecker also supports custom dictionaries. You can specify the custom dictionary with the CustomDictionary property.

For example, you can create a custom dictionary that accepts as correct any words that start with 'z'; therefore, any word that starts with 'z' will be correct.

1. From the Toolbox, add the C1SpellChecker component and RichTextBox control to your form.
   Note that the C1SpellChecker component will appear below the form, not on it.
2. Select the RichTextBox, and set the following properties:
   • Dock property to Fill.
   • SpellChecking on C1SpellChecker1 property to True.
3. To specify the custom dictionary, add the following code:

To write code in Visual Basic

Private _customDict As New MySpellDictionary()
Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
    C1SpellChecker1.CustomDictionary = _customDict
End Sub
Public Class MySpellDictionary
    Implements C1.Win.C1SpellChecker.ISpellDictionary
    Public Function Contains(ByVal word As String) As Boolean Implements C1.Win.C1SpellChecker.ISpellDictionary.Contains
        Return word.StartsWith("z", StringComparison.InvariantCultureIgnoreCase)
    End Function
End Class

To write code in C#

MySpellDictionary _customDict = new MySpellDictionary();
 
private void Form1_Load(object sender, EventArgs e)
{
    c1SpellChecker1.CustomDictionary = _customDict;
}
public class MySpellDictionary : C1.Win.C1SpellChecker.ISpellDictionary
{
    public bool Contains(string word)
    {
        return word.StartsWith("z", StringComparison.InvariantCultureIgnoreCase);
    }
}