luck vs good fortune

luck and good fortune both are nouns.

Word	Noun	Adjective	Verb	Adverb
luck	Yes	No	No	No
good fortune	Yes	No	No	No

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

luck: an unknown and unpredictable phenomenon that leads to a favorable outcome
good fortune: a stroke of luck

Other hyponyms of luck include fluke, good luck.

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

luck: your overall circumstances or condition in life (including everything that happens to you)
good fortune: an auspicious state resulting from favorable outcomes

Other hyponyms of luck include good luck, luckiness, providence, bad luck, ill luck, misfortune, tough luck, failure.

luck (noun)	good fortune (noun)
an unknown and unpredictable phenomenon that causes an event to result one way rather than another	a stroke of luck
an unknown and unpredictable phenomenon that leads to a favorable outcome	an auspicious state resulting from favorable outcomes
your overall circumstances or condition in life (including everything that happens to you)