[ vahy-roid ]
/ ˈvaɪ rɔɪd /


an infectious agent of plants similar to a virus but consisting of only a short, single strand of RNA without a protein coat.

Words nearby viroid

Origin of viroid

First recorded in 1946; vir(us) + -oid Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

British Dictionary definitions for viroid

/ (ˈvaɪrɔɪd) /


any of various infective RNA particles, smaller than a virus and known to cause some plant diseases

Word Origin for viroid

C20: from vir (us) + -oid
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Medicine definitions for viroid

[ vīroid′ ]


An infectious particle, smaller than a virus, that consists solely of a strand of RNA and is capable of causing disease in plants.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.

Science definitions for viroid

[ vīroid′ ]

An infectious agent that consists solely of a single strand of RNA and causes disease in certain plants. Viroids lack the protein coat (known as a capsid) of viruses and are the smallest known infectious agents. Containing only about 250 to 375 base pairs, they are much smaller than the smallest genomes of viruses and have no genes for encoding proteins. After invading a host cell, viroids are thought to mimic the cell's DNA, so that the cell's RNA polymerase replicates them in the nucleus. Viroids are believed to cause disease by interfering with the host cell's gene regulation. They are destructive to many important commercial plants, including potatoes, tomatoes, cucumbers, coconuts, and chrysanthemums.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.