POB vs compartment

POB and compartment both are nouns.

Word	Noun	Adjective	Verb	Adverb
POB	Yes	No	No	No
compartment	Yes	No	No	No

As nouns, compartment is a hypernym of POB; that is, compartment is a word with a broader meaning than POB:

POB: a numbered compartment in a post office where mail is put to be called for
compartment: a space into which an area is subdivided

POB (noun)	compartment (noun)
a numbered compartment in a post office where mail is put to be called for	a partitioned section, chamber, or separate room within a larger enclosed area
	a space into which an area is subdivided