This is in relation to the question "It's “1 degrees” or is it “1 degree” outside?". I have heard many people say that it is zero degrees outside. Is this correct, or is it 0 degree? The latter simply doesn't sound right.
From the OED,
Each of the marks denoting degrees of temperature on the scale of a thermometer, or the interval between two successive marks.
This usage of degree literally meant to measure against a thermometer containing markings that were called degrees. Thus, zero degrees is when the liquid inside did not rise to any of the marks above. one degree is to say the liquid inside rose to one mark.
Admittedly, we have now greatly expanded the concept of how we conceive of temperature, but such is the origin.