That which perceives, holds and reasons. A mind is known by what it does, since nobody has seen one directly.
Old English gemynd (memory, thought, intention), from Proto-Germanic *ga-mundiz, from the Proto-Indo-European root *men- (to think); that which perceives, holds and reasons.
A thing known only by its work — nobody has ever seen a mind directly, only the perceiving, holding and reasoning it leaves behind.