matrix /mā″triks, mat″riks/ [L, womb] , 1. an intercellular substance. 2. a basic substance from which a specific organ or kind of tissue develops. Also called ground substance. 3. a form used in shaping a tooth surface in dental procedures. 4. (in analytical chemistry) material of no interest in an analysis that may have an effect on the analysis. 5. a rectangular arrangement of elements into rows and columns, often used to display a digital image.