What is the X in X-mas?
c.1300, from Old French coral (12c., Modern French corail), from Latin corallium, from Greek korallion; perhaps of Semitic origin (cf. Hebrew goral "small pebble," Arabic garal "small stone"), originally just the red variety found in the Mediterranean, hence use of the word as a symbol of "red." Related: Coralline. Coral snake (1760) is so called for the red zones in its markings. Coral reef is attested from 1745.
Heb. ramoth, meaning "heights;" i.e., "high-priced" or valuable things, or, as some suppose, "that which grows high," like a tree (Job 28:18; Ezek. 27:16), according to the Rabbins, red coral, which was in use for ornaments. The coral is a cretaceous marine product, the deposit by minute polypous animals of calcareous matter in cells in which the animal lives. It is of numberless shapes as it grows, but usually is branched like a tree. Great coral reefs and coral islands abound in the Red Sea, whence probably the Hebrews derived their knowledge of it. It is found of different colours, white, black, and red. The red, being esteemed the most precious, was used, as noticed above, for ornamental purposes.