danger vs powder keg

danger and powder keg both are nouns.

Word	Noun	Adjective	Verb	Adverb
danger	Yes	No	No	No
powder keg	Yes	No	No	No

As nouns, powder keg is a hyponym of danger; that is, powder keg is a word with a more specific, narrower meaning than danger:

Other hyponyms of danger include endangerment, hazard, jeopardy, peril, risk, menace, threat.

danger (noun)	powder keg (noun)
a venture undertaken without regard to possible loss or injury	keg (usually made of metal) for gunpowder or blasting powder
a dangerous place	a potentially explosive state
the condition of being susceptible to harm or injury
a cause of pain or injury or loss