Use Mac OS command key in bash's bind command

According to one of the comments in Use CMD-mappings in console Vim, you cannot use the Command key in Terminal.app, though you could in iTerm2.

You're probably looking for modifier, like shift, control, e.g., something analogous to the alt or meta key.

In Terminal.app's keyboard preferences, you have an initial set of key definitions which use these modifiers—along with Option. You can alter these definitions, or add new ones.

Here are a couple of screenshots showing that dialog:

The second screenshot shows Option (alone, or in combination with other modifiers), but Command is not available for use by programs running in the terminal: