morphology vs petrology

morphology and petrology both are nouns.

Word	Noun	Adjective	Verb	Adverb
morphology	Yes	No	No	No
petrology	Yes	No	No	No

As nouns, petrology is a hyponym of morphology; that is, petrology is a word with a more specific, narrower meaning than morphology:

morphology: the branch of geology that studies the characteristics and configuration and evolution of rocks and land forms
petrology: the branch of geology that studies rocks: their origin and formation and mineral composition and classification

Other hyponyms of morphology include plate tectonic theory, plate tectonics, tectonics, lithology.

morphology (noun)	petrology (noun)
the branch of biology that deals with the structure of animals and plants	the branch of geology that studies rocks: their origin and formation and mineral composition and classification
studies of the rules for forming admissible words
the admissible arrangement of sounds in words
the branch of geology that studies the characteristics and configuration and evolution of rocks and land forms