Pa·rá River (pä-rä?) The southeast arm of the Amazon River estuary in northern Brazil. Divided from the rest of the river by Marajó Island, it is about 320 km (200 mi) long.American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.