coral (n.)

general name for the hard, calcareous skeleton excreted by certain marine polyps, c. 1300, from Old French coral (12c., Modern French corail), from Latin corallium, from Greek korallion, a word perhaps of Semitic origin (compare Hebrew goral "small pebble," Arabic garal "small stone").

Originally especially the red variety found in the Mediterranean, used ornamentally, hence "red, the (red) color of coral" (mid-15c.). As an adjective, "made of coral," mid-15c. The coral-snake (1760) is so called for the red zones in its markings. Coral-reef is attested from 1745 (see reef (n.1)).