diary vs web log

diary and web log both are nouns.

Word	Noun	Adjective	Verb	Adverb
diary	Yes	No	No	No
web log	Yes	No	No	No

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

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

Other hyponyms of diary include blog.

diary (noun)	web log (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