litmus vs acid-base indicator

litmus and acid-base indicator both are nouns.

Word	Noun	Adjective	Verb	Adverb
litmus	Yes	No	No	No
acid-base indicator	Yes	No	No	No

As nouns, acid-base indicator is a hypernym of litmus; that is, acid-base indicator is a word with a broader meaning than litmus:

litmus: a coloring material (obtained from lichens) that turns red in acid solutions and blue in alkaline solutions; used as a very rough acid-base indicator
acid-base indicator: an indicator that changes color on going from acidic to basic solutions

litmus (noun)	acid-base indicator (noun)
a coloring material (obtained from lichens) that turns red in acid solutions and blue in alkaline solutions; used as a very rough acid-base indicator	an indicator that changes color on going from acidic to basic solutions