precious coral vs red coral

precious coral and red coral both are nouns.

Word	Noun	Adjective	Verb	Adverb
precious coral	Yes	No	No	No
red coral	Yes	No	No	No

As nouns, precious coral and red coral are synonyms defined as:

precious coral and red coral: the hard stony skeleton of a Mediterranean coral that has a delicate red or pink color and is used for jewelry

Other synonyms of precious coral include coral.

precious coral (noun)	red coral (noun)
the hard stony skeleton of a Mediterranean coral that has a delicate red or pink color and is used for jewelry	corals of especially the Mediterranean having pink or red color used for ornaments and jewelry
	the hard stony skeleton of a Mediterranean coral that has a delicate red or pink color and is used for jewelry