panencephalitis vs cephalitis

panencephalitis and cephalitis both are nouns.

Word	Noun	Adjective	Verb	Adverb
panencephalitis	Yes	No	No	No
cephalitis	Yes	No	No	No

As nouns, cephalitis is a hypernym of panencephalitis; that is, cephalitis is a word with a broader meaning than panencephalitis:

panencephalitis: diffuse inflammation of the entire brain
cephalitis: inflammation of the brain usually caused by a virus; symptoms include headache and neck pain and drowsiness and nausea and fever (`phrenitis' is no longer in scientific use)

Other hypernyms of panencephalitis include encephalitis, phrenitis.

panencephalitis (noun)	cephalitis (noun)
diffuse inflammation of the entire brain	inflammation of the brain usually caused by a virus; symptoms include headache and neck pain and drowsiness and nausea and fever (`phrenitis' is no longer in scientific use)