soft coal vs bituminous coal

soft coal and bituminous coal both are nouns.

Word	Noun	Adjective	Verb	Adverb
soft coal	Yes	No	No	No
bituminous coal	Yes	No	No	No

As nouns, soft coal and bituminous coal are synonyms defined as:

soft coal and bituminous coal: rich in tarry hydrocarbons; burns readily with a smoky yellow flame

soft coal (noun)	bituminous coal (noun)
rich in tarry hydrocarbons; burns readily with a smoky yellow flame	rich in tarry hydrocarbons; burns readily with a smoky yellow flame