prions Definition

any of several small petrels (genus Pachyptila of the family Procellariidae) of the southern hemisphere that are bluish gray above and white below

prion protein; especially : an abnormal form of prion protein that in mammals includes pathogenic forms which arise sporadically, as a result of genetic mutation, or by transmission (as by ingestion of infected tissue) and which upon accumulation in the brain cause a prion disease (such as bovine spongiform encephalopathy or Creutzfeldt-Jakob disease)