box vs poor box

box and poor box both are nouns.

Word	Noun	Adjective	Verb	Adverb
box	Yes	No	Yes	No
poor box	Yes	No	No	No

As nouns, poor box is a hyponym of box; that is, poor box is a word with a more specific, narrower meaning than box:

box (noun)	poor box (noun)
a blow with the hand (usually on the ear)	box for collecting alms, especially one in a church
a (usually rectangular) container; may have a lid
separate partitioned area in a public place for a few people
private area in a theater or grandstand where a small group can watch the performance
the driver's seat on a coach
any one of several designated areas on a ball field where the batter or catcher or coaches are positioned
evergreen shrubs or small trees
the quantity contained in a box
a rectangular drawing
a predicament from which a skillful or graceful escape is impossible