In straitened circumstances and Lower-class

In straitened circumstances adjective - Not having enough money to pay for necessities.

Lower-class and in straitened circumstances are semantically related. In some cases you can use "Lower-class" instead an adjective phrase "In straitened circumstances".

Lower-class adjective - Belonging to the class of people of low social or economic rank.

In straitened circumstances and lower-class are semantically related. Sometimes you can use "In straitened circumstances" instead an adjective phrase "Lower-class".