Webster's English Dictionary

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impedance

im.ped.ance \im-'pe-d-*n(t)s\ n 1: the apparent opposition in an electrical 
   circuit to the flow of an alter nating current that is analogous to the 
   actual electrical resistance to a direct current and that is the ratio of 
   effective electromotive force to the effective current 2: the ratio of the 
   pressure to the volume displacement at a given surface  in a 
   sound-transmitting medium