† hypo-iˈodic, hyˈpiodic,a.Chem., Obs. [f. hypo- 5 + iodic.] In hypo-iodic acid, an old name for periodic oxide. 1854J. Scoffern in Orr's Circ.Sc., Chem. 368 Hypoiodic acid..IO4.1865–72Watts Dict.Chem. III. 297 Periodic oxide (Millon's Hypo-iodic acid) IO2 or I2O4.