The Collaborative International Dictionary of English v.0.48:

Ski \Ski\ (sk[=e]), n.; pl. skis (sk[=e]z). [Dan. ski; Icel.
   sk[imac][eth] a billet of wood. See Skid.]
   A long, flat, narrow runner made of wood, plastic or metal,
   curved upwards in front, having a fitting allowing it to be
   attached to the foot, and used for gliding or sliding over
   snow. Commonly used in the plural, to designate the pair.
   [Also spelled skee.]
   [Webster 1913 Suppl. +PJC] Skiagraph