Blavatsky
Original sense
An adept is a living human being who, by long discipline, has mastered the lower principles and can use occult laws that ordinary people cannot. Adeptship is earned, rare, and bodily. Blavatsky insisted her Teachers were men in physical bodies, not angels or the dead.
An Adept is one who has reached the summit of initiation — not a disembodied spirit, but a living man.
She distinguished the adept from the medium. The medium is a passive instrument of unseen influences; the adept is a trained, self-possessed operator. Chelaship is the apprenticeship that may, after many lives, lead there.