shearwater vs petrel

shearwater and petrel both are nouns.

Word	Noun	Adjective	Verb	Adverb
shearwater	Yes	No	No	No
petrel	Yes	No	No	No

As nouns, petrel is a hypernym of shearwater; that is, petrel is a word with a broader meaning than shearwater:

shearwater: long-winged oceanic bird that in flight skims close to the waves
petrel: relatively small long-winged tube-nosed bird that flies far from land

shearwater (noun)	petrel (noun)
long-winged oceanic bird that in flight skims close to the waves	relatively small long-winged tube-nosed bird that flies far from land