Binder
The glue in paint that holds the pigment particles together and sticks them to the surface.
Also: medium
Paint is pigment plus binder. The binder is what turns loose powder into a film that stays put. It also gives each kind of paint its name and character: linseed oil in oil paint, gum arabic in watercolour, egg yolk in tempera, acrylic resin in acrylics, lime in fresco, beeswax in encaustic. The binder affects how shiny the paint is, how fast it dries, how it ages and whether it yellows or cracks. The same pigment can look quite different in different binders.