black disease vs liver rot

black disease and liver rot both are nouns.

Word	Noun	Adjective	Verb	Adverb
black disease	Yes	No	No	No
liver rot	Yes	No	No	No

As nouns, black disease and liver rot are synonyms defined as:

black disease and liver rot: a disease of the liver (especially in sheep and cattle) caused by liver flukes and their by-products

Other synonyms of black disease include distomatosis, sheep rot.

black disease (noun)	liver rot (noun)
a disease of the liver (especially in sheep and cattle) caused by liver flukes and their by-products	a disease of the liver (especially in sheep and cattle) caused by liver flukes and their by-products