How do I disable Cmd-D in Terminal?
Assign a different key combination to Terminal’s Split Pane menu item:


Quit Terminal
Open System Preferences
Select the panel Keyboard from the second row
Select the tab Shortcuts at top center
Select App Shortcuts from the bottom of the list on the left
Click the + button, bottom center and a smaller panel appears
In the dropdown menu Application:, select Terminal


if Terminal isn’t on the list, scroll all the way to the bottom and select Other… (otherwise, skip to step 8 below)
when a dialog window appears, go to the folder Utilities and select Terminal

In the Menu Title: field, enter the text “Split Pane” without quotation marks, but with capital letters “S” and “P”
In the Keyboard Shortcut: field, enter your custom key combinationPro tips:


for a feature you hate, select a key combination you’ll never enter on accident, such as command ⌘‑control ⌃‑option ⌥‑shift ⇧‑D
select and hold down the modifier keys (that is, command ⌘, control ⌃, option ⌥, and shift ⇧) before you select the letter key (in this example, D)

Click Add
Restart your Mac and fire up Terminal
Become less unhappy