house wren vs wren

house wren and wren both are nouns.

Word	Noun	Adjective	Verb	Adverb
house wren	Yes	No	No	No
wren	Yes	No	No	No

As nouns, wren is a hypernym of house wren; that is, wren is a word with a broader meaning than house wren:

house wren: common American wren that nests around houses
wren: any of several small active brown birds of the Northern Hemisphere with short upright tails; they feed on insects

Other hypernyms of house wren include jenny wren.

house wren (noun)	wren (noun)
common American wren that nests around houses	any of several small active brown birds of the Northern Hemisphere with short upright tails; they feed on insects