Entry 2 senses · 2 variants Webster, 1913 Underdo · Un·der·do · IPA v. i. v. t. 01 v. i. To do less than is requisite or proper; -- opposed to overdo. 1. To do less than is requisite or proper; -- opposed to overdo. 02 v. t. To do less thoroughly than is requisite; specifically, to cook insufficiently; as, to underdo the meat; -- opposed to overdo. 1. To do less thoroughly than is requisite; specifically, to cook insufficiently; as, to underdo the meat; -- opposed to overdo.