luck vs good luck

luck and good luck both are nouns.

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

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

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

Other hyponyms of luck include fluke, good fortune.

As nouns, good luck is a hyponym of luck; that is, good luck 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 luck: an auspicious state resulting from favorable outcomes

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