All,
Just in case anyone else is looking for the answer to this I got a reply on the MS Technet forum with the answer...
You can use following registry key to disable "Look Up", "Synonyms" and "Translate" option and its sub-menu items, from right-click context menu.
[HKEY_CURRENT_USER\Software\Policies\Microsoft\offi ce\14.0\Word\DisabledCmdBarItemsList]
"TCID"="20392"
"TCID1"="30475"
"TCID2"="7021"
"TCID3"="16631"
"TCID4"="18355"
Make sure this registry key is applied to all concerned users (via log-on script or other means) since this a HKCU registry key. You can restrict access to registry editor to prevent users from changing these settings.
I didn't have any of the Key values below "Office", but if you manually create the keys and then add the String values listed all works perfectly.
Here's the technet forum link if anyone wants to take a nose there... Word 2010 - remove right-click context menu
Cheers,
LSDWho