n 1  :  the apparent opposition in an electrical circuit to the flow of an alternating 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  3  :  opposition to blood flow in the circulatory system .
 
 
 
Similar sounding terms:  im·po·tence  im·po·ten·cy 
 
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