-də(r) noun
( -s )
1.
a. : a substance added to a product especially in the capacity of a diluent, adulterant, or modifier: as
(1) or extender pigment : a colorless or white mineral pigment (as whiting) used with one or more other pigments usually to achieve certain physical properties (as improved surface characteristics or working properties in paint or printing ink) — called also filler, inert
(2) : a substance usually having some adhesive action (as flour) that is added to an adhesive for reducing the cost or sometimes for improving the viscosity
(3) : a substance (as a petroleum oil) used for increasing the bulk or improving the processing characteristics of a rubber compound, a plastic, or a resin
b. : expander 2
2. Britain : a teacher of university extension classes