nest vs bird's nest

nest and bird's nest both are nouns.

Word	Noun	Adjective	Verb	Adverb
nest	Yes	No	Yes	No
bird's nest	Yes	No	No	No

As nouns, bird's nest is a hyponym of nest; that is, bird's nest is a word with a more specific, narrower meaning than nest:

Other hyponyms of nest include beehive, hive, bird nest, birdnest, drey, mouse's nest, mouse nest, nidus.

nest (noun)	bird's nest (noun)
a kind of gun emplacement	nest where birds lay their eggs and hatch their young
furniture pieces made to fit close together
a gang of people (criminals or spies or terrorists) assembled in one locality
a cosy or secluded retreat
a structure in which animals lay eggs or give birth to their young

nest (verb)	bird's nest (verb)
fit together or fit inside
gather nests
move or arrange oneself in a comfortable and cozy position
inhabit a nest, usually after building