A large epithelial cell with an extremely acidophilic and granular cytoplasm, containing vast numbers of mitochondria; such cells may undergo neoplastic transformation. From the Greek word onkos meaning swelling, this cell type is found in parathyroid, salivary and thyroid glands. [ http://www.ncbi.nlm.nih.gov/pubmed/20013317 http://openisbn.com/search.php?q=0721662544&isbn=1/ GOC:tfm ]