add the function to your code, then follow the instructions below. the function will check to see if the selected replacement contains a definition and return just the word, otherwise it will just return what was passed as the argument.
Private Function GetWordWithOutBracketedText(SelectedReplacement As String) As String
if Strings.InStr(SelectedReplacement,"(") = 0 then
Dim arr() As String = Strings.Split(SelectedReplacement,"(")
then on the line that contains richtextbox1.selectedtext = kamau, change to
Richtextbox1.SelectedText = getwordwithoutbracketedtext(kamau)
let me know if this works. i dont have access to my computer at the moment, but i will double check for you when i get to my computer.