brown coal vs wood coal

brown coal and wood coal both are nouns.

Word	Noun	Adjective	Verb	Adverb
brown coal	Yes	No	No	No
wood coal	Yes	No	No	No

As nouns, brown coal and wood coal are synonyms defined as:

Other synonyms of brown coal include lignite.

brown coal (noun)	wood coal (noun)
intermediate between peat and bituminous coal	intermediate between peat and bituminous coal
	a carbonaceous material obtained by heating wood or other organic matter in the absence of air