Hydroxyurea: A drug that inhibits the synthesis of DNA and so is classified as an antimetabolite. Hydroxyurea is used to treat a number of diseases, including chronic myeloid leukemia (CML), polycythemia vera, carcinoma of the head and neck, ovary, and cervix, melanoma, and sickle cell disease. Hydroxyurea is taken orally and is inexpensive.