Stop Dictionary Pop-Up Window &lt; 3.5 GHz, 6-Core Mac Pro (2013 MacPro6,1) with 16GB RAM and D700 GPUs, running macOS 10.14.6 &gt;
Greetings, folks!
After reinstalling MacOS 10.14.6, whenever I type cmd-control-d, a window pops up with dictionary entries.
I have never seen this before (since 1986!) and have been unable to find where the command is controlled so that I can stop the pop-up window from appearing. I need this to stop, as I have used cmd-control-d for decades to generate a time-and-date stamp.
Any advice would be appreciated!
According to Apple documentation Mac keyboard shortcuts  ⌃+⌘+D is built-in document shortcut:

Document shortcuts
The behavior of these shortcuts may vary with the
app you're using.
/.../
Control-Command-D: Show or hide the definition of the selected word.

This shortcut is enabled irrespective whether System Preferences &gt; Keyboard &gt; Shortcuts &gt; Services &gt; Searching &gt; Look up in Dictionary assigned or not.
Keyboard shortcut for 'Look up in Dictionary' will open Dictionary app and not pop up window, so these are different things.
On my machine I observed 'varying behavior' as stated in documentation: I have not assigned shortcut but this key combination opens dictionary pop-up in Mail and Notes but not in Safari. Probably because MacOS doesn't consider webpage as 'document'.