n. 1. A type of igneous rock containing crystals.
2. The reddish or purplish color associated with this rock, often used poetically.
“Now sleeps the crimson petal, now the white;
Nor waves the cypress in the palace walk;
Nor winks the gold fin in the porphyry font”
-Alfred, Lord Tennyson
In Case You’re Interested…
The word itself hasn’t really changed over time. It comes to us through Middle English, from Latin, from Greek πόρφυρος (porphyros), ‘purple’.
The meaning, however, has changed by association throughout the years. The Greeks used it as the name for the stone, but the name is also connected to the “purple-whelk” (a mollusk) and the purple dye that could be made from its shell. Ancient Egypt had a quarry that was famous for producing this stone. It became commonly used by royalty for monuments and palaces, in the Roman and Byzantine empires, for example.
All this to say that the word is closely associated with royalty (see phrases like “being in the purple”). It has also been often used poetically, as a fancy way of saying “purple.”
It has several related words, including a particularly great one to use when speaking of heirs to a throne: porphyrogeniture (‘porphyry’ + ‘gen-‘, as in generation, genealogy, etc.). Also, the word ‘purple’ itself is actually derived from it; if you squint, you can kind of see it.