blog vs diary

blog and diary both are nouns.

Word	Noun	Adjective	Verb	Adverb
blog	Yes	No	Yes	No
diary	Yes	No	No	No

As nouns, diary is a hypernym of blog; that is, diary is a word with a broader meaning than blog:

blog: a shared on-line journal where people can post diary entries about their personal experiences and hobbies
diary: a daily written record of (usually personal) experiences and observations

Other hypernyms of blog include journal.

blog (noun)	diary (noun)
a shared on-line journal where people can post diary entries about their personal experiences and hobbies	a personal journal (as a physical object)
	a daily written record of (usually personal) experiences and observations

blog (verb)	diary (verb)
read, write, or edit a shared on-line journal