axle (n.) Look up axle at Dictionary.com
"pole or pin upon which a wheel revolves" (properly, the round ends of the axle-tree which are inserted in the hubs or naves of the wheels), 1630s, from Middle English axel-, from some combination of Old English eax and Old Norse öxull "axis," both from Proto-Germanic *akhsulaz (source also of Old English eaxl, Old Saxon ahsla, Old High German ahsala, German Achsel "shoulder"), from PIE *aks- "axis" (see axis, which is from the Latin cognate of this Germanic word). Found only in compound axle-tree before 14c.