In the 'BeforeClose' event of the 'ThisWorkbook' Module, put...
Private Sub Workbook_BeforeClose(Cancel As Boolean)
Cells.CheckSpelling CustomDictionary:="CUSTOM.DIC",
IgnoreUppercase:=False _
, AlwaysSuggest:=True, SpellLang:=1033
End Sub
I used the macro recorder to decide on the Spelling Language of 1033. This
is American English, General Style.
HTH,