fine linen: a costly, bright white cloth used for sacred and royal garments
This is the prized white fabric of the ancient world, imported from Egypt and reserved for people and objects of the highest honor. The great majority of its appearances are in the instructions for the tabernacle, where it forms the curtains, the screen at the entrance, and the garments of the priests. It is the cloth that surrounds holy space and clothes those who serve in it.
Outside worship, it marks status and wealth. Pharaoh dresses Joseph in it when he raises him to power, the capable woman of Proverbs makes her clothing from it, and the prophet Ezekiel pictures Jerusalem draped in it like a bride and Tyre using it for a ship's sail. Across all these settings the word points to one thing: the finest, whitest linen money could buy.
Because the fabric is always the same, this meaning holds together as a single sense. What changes from verse to verse is only what the linen is made into, a curtain, a robe, or a sail, not what the word itself means.