-seal off (a place) to prevent people from coming in or out
Block (the base of blockade)
Definition: make the movement or flow in difficult or impossible
-Ade (suffix of blockade)
Below is a picture of a blockade
The word block means to keep out or in. When you add -ade (action) to it, it becomes blockade. Putting these two together turns block into an action, blockade.
The blockade is preventing all trade to and from the port.