petrology vs lithology

petrology and lithology both are nouns.

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

As nouns, petrology and lithology are synonyms defined as:

petrology and lithology: the branch of geology that studies rocks: their origin and formation and mineral composition and classification

petrology (noun)	lithology (noun)
the branch of geology that studies rocks: their origin and formation and mineral composition and classification	the branch of geology that studies rocks: their origin and formation and mineral composition and classification