Don't bother trying to convince Trotsky the labor-capital system works; he's a dyed in the wool Communist.

To be "dyed in the wool" means that the person or thing is so deeply ingrained with a certain characteristic or belief that they are inflexible. It is usually used as a passing remark, though it almost always carries the subtle implication of closedmindedness.

Three divergent theories (though similar in concept) have emerged regarding the etymology of the phrase:

  1. The natural colors of a sheep's wool were impossible to completely subvert - for example, a black sheep's wool would be darker than a white sheep's wool when dyed the same color. Thus, "dyed in the wool" implies that some features are inherent and immutable in people.
  2. Pieces of clothing that were made with pre-dyed wool yarn often had a richer tone than pieces dyed after they had been sewn together. This was because certain areas of the fabric weren't hit as thoroughly by the dye. Thus, a stronger sentiment or idea might be described as being "dyed in the wool."
  3. Clothes and blankets made of wool generally tend to have a longer-lasting colorfast ability. Thus, something "dyed in the wool" tends to be more unwavering and consistent over time.

Although wool has of course had its own venerable place in the history of mankind, the phrase did not see common usage until the late 16th century. By the 1800s it was being used almost exclusively to allude to people's political and ideological beliefs. Today, the phrase is in declining use, though you'll see it pop up from time to time. And now you know ... the rest of the story.