Apart from the obvious facial hair definition, Chambers gives the answer as "a fastening or clasp" which doesn't seem to fit with "twirl around" - what was your thinking?
Sorry, maybe I got a bit carried away.
I was thinking of a tachometer which measures rpm.
Maybe I'm way off the mark.
It will be interesting to read fifteensquared next week.
Ah! I see what you mean - if one was going really fast, it would "twirl" around and be quite "hairy"/scary. I think that might be it Rossim, otherwise why would there be an apostrophe at the end.