ill luck vs hard knocks

ill luck and hard knocks both are nouns.

Word	Noun	Adjective	Verb	Adverb
ill luck	Yes	No	No	No
hard knocks	Yes	No	No	No

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

Other hyponyms of ill luck include weakness, adversity, hardship, gutter, sewer, toilet, hard cheese.

ill luck (noun)	hard knocks (noun)
an unfortunate state resulting from unfavorable outcomes	a state of misfortune or affliction