murk vs fug

murk and fug both are nouns.

Word	Noun	Adjective	Verb	Adverb
murk	Yes	No	Yes	No
fug	Yes	No	No	No

As nouns, fug is a hyponym of murk; that is, fug is a word with a more specific, narrower meaning than murk:

murk: an atmosphere in which visibility is reduced because of a cloud of some substance
fug: (British informal) an airless smoky smelly atmosphere

murk (noun)	fug (noun)
an atmosphere in which visibility is reduced because of a cloud of some substance	(British informal) an airless smoky smelly atmosphere

murk (verb)	fug (verb)
make dark, dim, or gloomy