castile : Idioms & Phrases

• noun a good hard soap made from olive oil and sodium hydroxide
  

WordNet

Cas"tile soap"

Etymology

From Castile, or Castilia, a province in Spain, from which it originally came.

Definitions

1. A kind of fine, hard, white or mottled soap, made with olive and soda; also, a soap made in imitation of the above-described soap.

Webster 1913