Clairvoyance entered the modern vocabulary through animal magnetism. In the 1780s the Marquis de Puysegur, a student of Franz Mesmer, found that some magnetised subjects fell into a deep artificial somnambulism in which they seemed to describe objects, illnesses, or distant scenes they could not have perceived normally. French practitioners called the faculty "clairvoyance," clear seeing, and it became a standard claim of magnetic healers through the nineteenth century: a somnambulist might diagnose a patient's illness by "seeing" inside the body, or locate a lost object at a distance.
The claim travelled easily into spiritualism after 1848, where clairvoyant description of the deceased or of unseen rooms became a staple platform skill for mediums, and into the broader occult revival, where clairvoyance was folded into theosophical and esoteric teaching about subtle senses beyond the physical five. By the time organised psychical research began in 1882, clairvoyance already had a century of anecdote behind it, entirely undocumented by controlled observation, which is precisely what the Society for Psychical Research set out to supply. The distinction researchers draw between clairvoyance and telepathy, perceiving an object directly versus reading another mind that knows the object, has mattered enormously to experimental design ever since, because it determines whether a sender is needed at all.