Definitions for viroidˈvaɪ rɔɪd
Random House Webster's College Dictionary
an infectious agent of plants similar to a virus but consisting of only a short, single strand of RNA without a protein coat.
the smallest of viruses; a plant virus with its RNA arranged in a circular chromosome without a protein coat
plant pathogens, of the order Viroidales, that consist of just a short section of RNA but without the protein coat typical of viruses
human pathogen, most notably hepatitis D.