A ski is a narrow strip of semi-rigid material worn underfoot to glide over snow. Substantially longer than wide and characteristically employed in pairs, skis are attached to ski boots with ski bindings, with either a free, lockable, or partially secured heel. For climbing slopes, ski skins (originally made of seal fur, but now made of synthetic materials) can be attached at the base of the ski. Originally intended as an aid to travel over snow, they are now mainly used recreationally in the sport of skiing. Etymology and usage The word ski comes from the Old Norse word which means "cleft wood", "stick of wood" or "ski". In Old Norse common phrases describing skiing were fara á skíðum (to travel, move fast on skis), renna (to move swiftly) and skríða á skíðum (to stride on skis). In modern Norwegian the word ski has largely retained the Old Norse meaning in words for split firewood, wood building materials (such as bargeboards) and roundpole fence. In Norwegian this word is usually pronounced . In Swedish, another language evolved from Old Norse, the word is (plural, ; singular: ). English and French use the original Norwegian spelling , and modify the pronunciation. Before 1920, English often called them skee and snow-shoe. In Italian, it is pronounced similarly to Norwegian, but the spelling is modified accordingly: . Portuguese and Spanish adapt the word to their linguistic rules: and . In German, spellings Ski and Schi are in use, both pronounced . In Dutch, the word is and the pronunciation was originally as in Norwegian, but since approximately the 1960s changed to . In Welsh the word is spelled sgi. Many languages make a verb form out of the noun, such as to ski in English, in French, in Spanish and Portuguese, in Italian, in Dutch, or or (as above also or ) in German. Norwegian and Swedish do not form a verb from the noun. Finnish has its own ancient words for skis and skiing: "ski" is and "skiing" is . The word suksi goes back to the Proto-Uralic period, with cognates such as Erzya soks, Mansi tåut and Nganasan tuta. The Sami also have their own words for "skis" and "skiing": for example, the Lule Sami word for "ski" is and skis are called . The Sami use for the verb "to ski" (the term may date back to 10,000 years before