1. n. 
A salt formed when a fatty acid reacts with a metal oxide or hydroxide. Fatty acids and lime, Ca(OH)2, form emulsifiers for oil muds. Fatty acids reacted with sodium hydroxide [NaOH] or potassium hydroxide [KOH] are laundry soaps, some used as foamers for air drilling. Fatty acids and aluminum hydroxide form soaps used as greases and as defoamer chemicals.
See: aluminum stearate, calcium hydroxide, calcium oxide, colloid, emulsifier, fatty acid, greasing out, invert-emulsion oil mud, low-colloid oil mud, lubricant, neutralization, oil mud, oil-mud emulsifier, soap, water-mud emulsifier