The term 'completely permeate' can be defined as to SATURATE, which is an 8 letter word. To SATURATE means to fill or soak something completely with a liquid or other substance. This term is often used in the context of water seeping through a porous material, such as soil, and filling it up. It can also be used to describe how a gas or vapor can fill a space. In either case, the idea is that the substance has filled the entire area, leaving no gaps.