bituminous coal vs soft coal

bituminous coal and soft coal both are nouns.

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

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

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

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