London paste (Med.), a paste made of caustic soda and unslacked lime; -- used as a caustic to destroy tumors and other morbid enlargements. -- London pride. (Bot.) (a) A garden name for Saxifraga umbrosa, a hardy perennial herbaceous plant, a native of high lands in Great Britain. (b) A name anciently given to the Sweet William. Dr. Prior. -- London rocket (Bot.), a cruciferous plant (Sisymbrium Irio) which sprung up in London abundantly on the ruins of the great fire of 1667.