philology vs lexicology

philology and lexicology both are nouns.

Word	Noun	Adjective	Verb	Adverb
philology	Yes	No	No	No
lexicology	Yes	No	No	No

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

philology: the humanistic study of language and literature
lexicology: the branch of linguistics that studies the lexical component of language

Other hyponyms of philology include dialectology, classical philology.

philology (noun)	lexicology (noun)
the humanistic study of language and literature	the branch of linguistics that studies the lexical component of language