viva vs oral examination

viva and oral examination both are nouns.

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

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

viva and oral examination: an examination conducted by spoken communication

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

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