journal vs diary

journal and diary both are nouns.

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

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

Other hyponyms of journal include daybook, ledger.

As nouns, journal and diary are synonyms defined as:

journal and diary: a daily written record of (usually personal) experiences and observations

journal (noun)	diary (noun)
the part of the axle contained by a bearing	a personal journal (as a physical object)
a record book as a physical object	a daily written record of (usually personal) experiences and observations
a periodical dedicated to a particular subject
a daily written record of (usually personal) experiences and observations
a ledger in which transactions have been recorded as they occurred