field hut vs Nissen hut

field hut and Nissen hut both are nouns.

Word	Noun	Adjective	Verb	Adverb
field hut	Yes	No	No	No
Nissen hut	Yes	No	No	No

As nouns, Nissen hut is a hyponym of field hut; that is, Nissen hut is a word with a more specific, narrower meaning than field hut:

field hut: temporary military shelter
Nissen hut: a prefabricated hut of corrugated iron having a semicircular cross section

Other hyponyms of field hut include Quonset hut.

field hut (noun)	Nissen hut (noun)
temporary military shelter	a prefabricated hut of corrugated iron having a semicircular cross section