diary vs blog

diary and blog both are nouns.

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

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

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

Other hyponyms of diary include web log.

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

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