di-ˈiodo-, di-ˈiod-Chem.[f. di-2 + -iodo-.]Having two atoms of iodine replacing two of hydrogen, as di-iodomethane CH2I2. ˌdiiodoˈtyrosine, an iodine-containing derivative of tyrosine, C9H9NO3I2, which is the precursor of thyroxine in the body and the compound into which iodine is first converted when absorbed by the thyroid gland from the blood.1869Roscoe Elem.Chem. 417 Prepared by the action of caustic potash on di-bromo- or di-iodo-salicylic acid.1877Watts Fownes' Chem. II. 68 Di-iodomethane..crystallises in colourless shining laminæ of specific gravity 3·34.1927Biochem.Jrnl. XXI. 170 It is highly probable that thyroxine is formed in nature by the coupling of two molecules of diiodotyrosine with the loss of one side chain.1949Blakiston's New Gould Med.Dict. 297/2 Diiodotyrosine, C9H9O3NI2. A substance found in skeletons of corals, sponges, and other marine organisms. It..has been used in hyperthyroidism.1964L. Martin Clinical Endocrinol. (ed. 4) iii. 122 In goitrous cretins..the thyroid may be unable to trap iodide from the blood, or..to couple molecules of diiodotyrosine to form thyroxine.