The Collaborative International Dictionary of English v.0.48:

Sublease \Sub"lease`\, n. (Law)
   A lease by a tenant or lessee to another person; an
   underlease. --Bouvier.
   [1913 Webster]

WordNet (r) 3.0 (2006):

sublease
    n 1: a lease from one lessee to another [syn: sublease,
         sublet]
    v 1: lease or rent all or part of (a leased or rented property)
         to another person; "We sublet our apartment over the
         summer" [syn: sublet, sublease]

Moby Thesaurus II by Grady Ward, 1.0:

82 Moby Thesaurus words for "sublease":
   adverse possession, alodium, bareboat charter, burgage, charter,
   claim, colony, de facto, de jure, dependency, derivative title,
   farm, farm out, fee fief, fee position, fee simple,
   fee simple absolute, fee simple conditional, fee simple defeasible,
   fee simple determinable, fee tail, feodum, feud, fiefdom,
   frankalmoign, free socage, freehold, gavelkind, having title to,
   hire, hire out, hiring, hold, holding, job, knight service,
   lay fee, lease, lease out, lease-back, lease-lend, leasehold,
   legal claim, legal possession, lend-lease, let, let off, let out,
   mandate, occupancy, occupation, original title, owning, possessing,
   possession, preoccupancy, preoccupation, prepossession,
   prescription, property, property rights, proprietary rights, rent,
   rent out, rental, seisin, socage, squatting, sublet, subrent,
   tenancy, tenantry, tenure, tenure in chivalry, title, underlease,
   underlet, undertenancy, usucapion, villein socage, villeinhold,
   villenage