expression.UserDict
expression Required. An expression that returns one of the objects in the Applies To list.
Example
This example instructs Microsoft Excel to create custom dictionary called "Custom1.dic" in the spelling options feature and notifies the user.
Sub SpecialWord()
Application.SpellingOptions.UserDict = "Custom1.dic"
MsgBox "The custom dictionary is currently set to: " _
& Application.SpellingOptions.UserDict
End Sub