referendum
Pronunciation: /ˌrɛfəˈrɛndəm/
noun ( plural referendums or referenda /-də/)

Origin:
mid 19th century: from Latin, gerund ( 'referring') or neuter gerundive ( 'something to be brought back or referred') of referre (see refer)

Spelling help
The plural of referendum can be spelled either referenda (like the original Latin) or referendums.