bad luck vs tragedy

bad luck and tragedy both are nouns.

Word	Noun	Adjective	Verb	Adverb
bad luck	Yes	No	No	No
tragedy	Yes	No	No	No

As nouns, tragedy is a hyponym of bad luck; that is, tragedy is a word with a more specific, narrower meaning than bad luck:

bad luck: unnecessary and unforeseen trouble resulting from an unfortunate event
tragedy: an event resulting in great loss and misfortune

bad luck (noun)	tragedy (noun)
unnecessary and unforeseen trouble resulting from an unfortunate event	drama in which the protagonist is overcome by some superior force or circumstance; excites terror or pity
an unpredictable outcome that is unfortunate	an event resulting in great loss and misfortune
an unfortunate state resulting from unfavorable outcomes