The Collaborative International Dictionary of English v.0.48:
Diagrammatic \Di`a*gram*mat"ic\, a. Pertaining to, or of the nature of, a diagram; showing by diagram. -- Di`a*gram*mat"ic*ly, adv. [1913 Webster]WordNet (r) 3.0 (2006):
diagrammatic adj 1: shown or represented by diagrams [syn: diagrammatic, diagrammatical]