n 1  :  an abnormally hollow condition or sagging of the back found esp. in horses : also  :  a back so shaped  2  :  LORDOSIS  3  :  a copper-deficiency disease of young or newborn lambs that is marked by demyelination of the brain resulting in weakness, staggering gait, and collapse and is almost universally fatal but is readily preventable by copper supplementation of the diet of the pregnant ewe sway*backed adj 
 
   
 
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