sullen vs dour

sullen and dour both are adjectives.

Word	Noun	Adjective	Verb	Adverb
sullen	No	Yes	No	No
dour	No	Yes	No	No

As adjectives, sullen and dour are synonyms defined as:

Other synonyms of sullen include dark, glowering, glum, moody, morose, saturnine, sour.

sullen (adjective)	dour (adjective)
darkened by clouds	showing a brooding ill humor
showing a brooding ill humor	stubbornly unyielding
	harshly uninviting or formidable in manner or appearance