To penetrate means to pass into or through something, often something that resists or blocks the way. When a nail penetrates a piece of wood, it pushes through the surface and into the material. When sunlight penetrates thick clouds on a gray day, the rays break through and reach the ground below.

The word suggests overcoming a barrier or resistance. Scientists study how certain medications can penetrate cell walls to deliver healing compounds. A submarine penetrates deep ocean waters, pushing through pressure that would crush most vessels. When you're reading a difficult book and finally penetrate its meaning, you've broken through confusion to reach understanding.

The word penetrating can describe something sharp and intense, like a penetrating cold that seems to cut right through your jacket, or a penetrating question that gets to the heart of an issue. A teacher with a penetrating gaze seems to see right through excuses and spot the truth. When something is described as penetrating, it has a quality of going deeper than surface level, reaching into places that are normally protected or hidden.