watchdog vs guardian

watchdog and guardian both are nouns.

Word	Noun	Adjective	Verb	Adverb
watchdog	Yes	No	No	No
guardian	Yes	No	No	No

As nouns, guardian is a hypernym of watchdog; that is, guardian is a word with a broader meaning than watchdog:

watchdog: a guardian or defender against theft or illegal practices or waste
guardian: a person who cares for persons or property

Other hypernyms of watchdog include defender, protector, shielder.

watchdog (noun)	guardian (noun)
a dog trained to guard property	a person who cares for persons or property
a guardian or defender against theft or illegal practices or waste