posthouse vs hostel

posthouse and hostel both are nouns.

Word	Noun	Adjective	Verb	Adverb
posthouse	Yes	No	No	No
hostel	Yes	No	No	No

As nouns, hostel is a hypernym of posthouse; that is, hostel is a word with a broader meaning than posthouse:

Other hypernyms of posthouse include auberge, hostelry, inn, lodge.

posthouse (noun)	hostel (noun)
an inn for exchanging post horses and accommodating riders	inexpensive supervised lodging (especially for youths on bicycling trips)
	a hotel providing overnight lodging for travelers