dye [OE] Both main uses of dye, ‘a substance used to add or change colour’ and ‘to add a colour to’, are recorded in Old English. The basis of dyed in the wool [LME], ‘unchanging in a belief or opinion’, is the fact that yarn dyed in its raw state, before it is woven into a piece of fabric, has a much more even and permanent colour. The practice goes back many centuries, and the sense of ‘unchanging’ is also very old. Nowadays people often use the expression to refer to someone’s political or sporting affiliation.