Entry 2 senses · 2 variants Webster, 1913 Underdose · Un·der·dose · IPA n. v. t. & i. 01 n. A dose which is less than required; a small or insufficient dose. 1. A dose which is less than required; a small or insufficient dose. 02 v. t. & i. To give an underdose or underdoses to; to practice giving insufficient doses. 1. To give an underdose or underdoses to; to practice giving insufficient doses.