To spend whatever money is necessary to achieve the best possible result, without concern for cost.
This phrase emerged in English during the 17th century, evolving from the older construction 'to spare no cost.' The word 'spare' here means 'to refrain from using' or 'to hold back,' so the phrase literally means 'don't hold back any expense.' It became particularly popular in the 19th century as consumer culture and luxury goods became more prominent in society.
The phrase reveals an interesting linguistic quirk - 'spare' typically means to save or go without, but here it means the opposite: don't save anything. This creates a subtle irony where the act of not sparing (saving) money demonstrates the ultimate form of not being sparing (stingy) with resources.
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