turquoise vs greenish blue

turquoise and greenish blue both are nouns.

Word	Noun	Adjective	Verb	Adverb
turquoise	Yes	No	No	No
greenish blue	Yes	No	No	No

As nouns, turquoise and greenish blue are synonyms defined as:

Other synonyms of turquoise include aqua, aquamarine, cobalt blue, peacock blue.

turquoise (noun)	greenish blue (noun)
a shade of blue tinged with green	a shade of blue tinged with green
a blue to grey green mineral consisting of copper aluminum phosphate