gateway: a large gate structure, or the entrance-passage that runs through it
πυλών names a gateway as a built structure, not merely the panel that swings shut. Where the plain word for a gate or door (πύλη) points to the barrier itself, πυλών points to the whole entrance: the massive portal set into a city wall, or the roofed passage that leads from the street door of a house through to the inner courtyard.
In Revelation the word describes the twelve monumental gates of the New Jerusalem, each a single pearl, standing open day and night. In the Gospels and Acts it more often describes an ordinary household entrance: the covered passage where Peter warmed himself and slipped out, the doorway where a servant girl came to answer a knock, the spot where a beggar was laid to catch the people passing in and out.
Both settings share one idea, the point of passage through a wall or the front of a building, so a translator can usually reach for "gate" or "gateway." What shifts is the scale: a towering city portal in one place, a modest entryway or porch in another.