compartment vs POB

compartment and POB both are nouns.

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

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

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

Other hyponyms of compartment include cell, cubbyhole, pigeonhole, call box, letter box, PO Box, Post-Office box.

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