Porthole (noun)

A round window in the side of a ship or aircraft, typically one that can be opened for ventilation or to admit light.

Origin:

Mid-16th century: from port + hole.

Examples:

1. He looked out of the porthole.
2. The cabin had two portholes that let in plenty of light.
3. The ship was equipped with portholes that could be opened for ventilation.
4. He peered through the porthole, trying to catch a glimpse of the shore.
5. The porthole provided a view of the ocean as the ship sailed.