In KM 1.1.4 of KM 1.5a2 go in the menu bar to
Edit > Preferences (possibly AdvancedPreferences) >
Browsing > Finding Websites > Search Engines
Push there the button "Add" .
A dialog will spring up : "Add Search Engine"
Into the line "Caption" write :
DRAE diccionario
Into the line URL write :
http://www.rae.es/
(not just www.rae.es, but copy the content of the link by
right click "Copy Link URL").
Push the button "OK".
Go to the tab "Web Search".
Push the button "Add Entry".
A line will appear "Remove Entry".
Open the dropdown menu of this line (the down arrow on the right).
Select the line : DRAE diccionario
Push the button Next or Close and close Preferences.
Possibly a restart of the browser is necessary.
Note : This will not work in my K-Meleon Linux variations.
I hope that you will succeed. I am here on Linux and can't
check it now in Windows, but it should work ok.
Fred