Equivalent of Dragon NaturallySpeaking's HeardWord function in Dragon Dictate 4
It can depends in which application you dictate. 

The online help is accessible by clicking on the Dragon icon in the menu bar. 

Or click here: http://www.nuance.com/products/help/dragon/dragon-for-mac/enx/Content/GetStarted.htm

Else, there is the Commands manager in the same menu in the menu bar.

On Mac, you can use Applescript with Dragon Command manager.