tough luck vs weakness

tough luck and weakness both are nouns.

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

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

Other hyponyms of tough luck include adversity, hard knocks, hardship, gutter, sewer, toilet, hard cheese.

tough luck (noun)	weakness (noun)
an unfortunate state resulting from unfavorable outcomes	the property of lacking physical or mental strength; liability to failure under pressure or stress or strain
	powerlessness revealed by an inability to act
	a penchant for something even though it might not be good for you
	a flaw or weak point
	the condition of being financially weak