Entry 1 sense Webster, 1913 Dimidiation /dĭmĭ'dĭāʹshən/ · Di·mid·i·a·tion · IPA /dɪˌmɪdɪˈeɪʃən/ 01 n. The act of dimidiating or halving; the state of being dimidiate. 1. The act of dimidiating or halving; the state of being dimidiate.