There used to be a way to remove it, but I do not see it any longer. Under Menu Preferences, in the tab Applications, I unchecked 'search for applications', but it does it anyway if you type a term not in the menu (I.E. 'cad'). If it is a common term it takes almost a full minute before it will respond again because it is searching all the repositories.
It also wants to search google, wikipedia, and the dictionary. I know I had figured out a way to turn this off before, but I tried several terms on here and can not find it and neither the manual or synaptic gave me any clues either. Was this ability removed?

