There are four syllables in the word "glossolalia."

She began speaking in glossolalia during the religious ceremony, using unintelligible sounds and syllables.

Vincenzo Scippa has written:

'La glossolalia nel Nuovo Testamento' -- subject(s): Bible, Biblical teaching, Criticism, interpretation, Glossolalia

Alt. of Glossolaly

You're probably thinking of "glossolalia", though it's not really synonymous with Pentecost. Glossolalia is basically speaking in tongues or an unknown language, which is what they did on the Day of Pentecost -- and many do today. Another word for it is xenoglossia.