oral examination vs viva

oral examination and viva both are nouns.

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

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

oral examination and viva: an examination conducted by spoken communication

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

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