Entry 1 sense Webster, 1913 Dieter /dēt'-ẽr/ · Di·et·er · IPA /dˈiːtər/ 01 n. One who diets; one who prescribes, or who partakes of, food, according to hygienic rules. 1. One who diets; one who prescribes, or who partakes of, food, according to hygienic rules.