Wikipedia
The arbitristas—a Spanish word meaning "projectors"—were a group of reformers in 17th century Spain. The arbitristas were concerned about the decline of the economy of Spain and proposed a number of measures to reverse it. From John H. Elliott's Imperial Spain:
The arbitristas proposed that Government expenditure should be slashed, that the tax-system in Castile should be overhauled, and the other kingdoms of the Monarchy be called upon to contribute more to the royal exchequer; that immigrants should be encouraged to re-populate Castile; that fields should be irrigated, rivers be made navigable, and agriculture and industry be protected and fostered.
Some arbitristas argued that the large quantities of silver and gold arriving from the mines in Spain's American colonies was doing great damage to the Spanish economy.
The Spanish valido Count-Duke of Olivares was strongly influenced by the arbitristas.
People like the writer Francisco de Quevedo dismissed the arbitristas with ridicule by satirising their more outlandish schemes. This attitude is still present in the colloquial meaning of the word.