Sleigh - a Dutch word with an alternative spelling of sley - an old English spelling (from before 1050s) is also associated weaving fabric. Sleighing (sleying) the reed was to draw the warp ends through the heddle eyes of the harness...are you still with me?
No, me neither - I had to look it up !
And in simplified terms, it is the action of pulling the yarn through the reed (the comb) with the sley (hook) which, if you look, is the same shape as the runners on a sleigh!
So now you know!
Joining in with Julie and her Advent Calendar 2018