tragedy vs bad luck

tragedy and bad luck both are nouns.

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

As nouns, bad luck is a hypernym of tragedy; that is, bad luck is a word with a broader meaning than tragedy:

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

Other hypernyms of tragedy include misfortune.

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