viva voce vs oral examination

viva voce and oral examination both are nouns.

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

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

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

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

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

viva voce (adverb)	oral examination (adverb)
orally