luck vs tough luck

luck and tough luck both are nouns.

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

As nouns, tough luck is a hyponym of luck; that is, tough 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)
tough luck: an unfortunate state resulting from unfavorable outcomes

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

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