penniless vs hard up

penniless and hard up both are adjectives.

Word	Noun	Adjective	Verb	Adverb
penniless	No	Yes	No	No
hard up	No	Yes	No	No

As adjectives, penniless and hard up are synonyms defined as:

Other synonyms of penniless include impecunious, in straitened circumstances, penurious, pinched.

penniless (adjective)	hard up (adjective)
not having enough money to pay for necessities	not having enough money to pay for necessities