oral examination vs viva voce

oral examination and viva voce both are nouns.

Word	Noun	Adjective	Verb	Adverb
oral examination	Yes	No	No	No
viva voce	Yes	No	No	Yes

As nouns, oral examination and viva voce are synonyms defined as:

oral examination and viva voce: an examination conducted by spoken communication

Other synonyms of oral examination include oral, oral exam, viva.

oral examination (noun)	viva voce (noun)
an examination conducted by spoken communication	an examination conducted by spoken communication

oral examination (adverb)	viva voce (adverb)
	orally