1 : thyroid hormone similar to thyroxine but with one less iodine atom per molecule and produced in smaller quantity; exerts the same biological effects as thyroxine but is more potent and briefer
2 : hormone produced by the thyroid glands to regulate metabolism by controlling the rate of oxidation in cells; "thyroxine is 65% iodine"
3 : a base found in DNA (but not in RNA) and derived from pyrimidine; pairs with adenine
