n, pl  -ties  1  :  the quality or state of a body that makes it impervious to the rays of light : broadly  :  the relative capacity of matter to obstruct by absorption or reflection the transmission of radiant energy (as x-radiation, radio waves, infrared radiation, or sound)  2  :  an opaque spot in a normally transparent structure (as the lens of the eye) .
 
 
 
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