The Collaborative International Dictionary of English v.0.48:

Inpatient \In"pa`tient\, n.
   A patient who receives lodging and food, as well as
   treatment, in a hospital or an infirmary; -- distinguished
   from outpatient.
   [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

inpatient
    n 1: a patient who is residing in the hospital where he is being
         treated [syn: inpatient, inmate] [ant: outpatient]

Moby Thesaurus II by Grady Ward, 1.0:

40 Moby Thesaurus words for "inpatient":
   addressee, apoplectic, arthritic, artist-in-residence, case,
   consumptive, denizen, dweller, dyspeptic, epileptic, habitant,
   house detective, incumbent, incurable, inhabitant, inhabiter,
   inmate, intern, invalid, live-in maid, locum tenens, occupant,
   occupier, outpatient, patient, residencer, resident,
   resident physician, residentiary, resider, rheumatic, shut-in,
   sick person, sojourner, spastic, sufferer, tenant, terminal case,
   the sick, valetudinarian