adj 1  :  not easily penetrated  :  not easily yielding to pressure  2 a  of liquor  :  strongly alcoholic : specif  :  having an alcoholic content of more than 22.5 percent  b  :  characterized by the presence of salts (as of calcium or magnesium) that prevent lathering with soap < water>   3  :  of or relating to radiation of relatively high penetrating power < X rays>   4 a  :  physically fit <in good condition>   b  :  resistant to stress (as disease)  5  :  being at once addictive and gravely detrimental to health <such drugs as heroin>   6  :  resistant to biodegradation < detergents>  < pesticides like DDT>  hard*ness n 
 
 
 
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