1. n. []

A material added to a drilling fluid to perform one or more specific functions, such as a weighting agent, viscosifier or lubricant.

See related terms: barite,  bentonite,  carboxymethylcellulose,  hematite,  lignite,  lignosulfonate,  mudding up,  native-solids mud,  viscosity,  weighting material,  XC polymer