n 1  :  the characteristic vertebrate organ of hearing and equilibrium consisting in the typical mammal of a sound-collecting outer ear separated by the tympanic membrane from a sound-transmitting middle ear that in turn is separated from a sensory inner ear by membranous fenestrae  2 a  :  the external ear of humans and most mammals  b  :  a human earlobe <had her s pierced>   3 a  :  the sense or act of hearing  b  :  acuity of hearing .
 
 
 
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