Entry 1 sense Webster, 1913 Diagrammatic /dīˌ-əg-rəm-ăt'-ĭk/ · Di·a·gram·mat·ic · IPA /dˌaɪəɡrəmˈætɪk/ 01 a. Pertaining to, or of the nature of, a diagram; showing by diagram. 1. Pertaining to, or of the nature of, a diagram; showing by diagram.