hard up vs in straitened circumstances

hard up and in straitened circumstances both are adjectives.

Word	Noun	Adjective	Verb	Adverb
hard up	No	Yes	No	No
in straitened circumstances	No	Yes	No	No

As adjectives, hard up and in straitened circumstances are synonyms defined as:

hard up and in straitened circumstances: not having enough money to pay for necessities

Other synonyms of hard up include impecunious, penniless, penurious, pinched.

hard up (adjective)	in straitened circumstances (adjective)
not having enough money to pay for necessities	not having enough money to pay for necessities