The Collaborative International Dictionary of English v.0.48:

Clearstory \Clear"sto`ry\ (kl[=e]r"st[=o]`r[y^]), Clerestory
\Clere"sto`ry\, n. (Arch.)
   The upper story of the nave of a church, containing windows,
   and rising above the aisle roofs.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Clerestory \Clere"sto`ry\ (kl[=e]r"st[=o]`r[y^]), n.
   Same as Clearstory.
   [1913 Webster]

WordNet (r) 3.0 (2006):

clerestory
    n 1: part of an interior wall rising above the adjacent roof
         with windows admitting light [syn: clerestory,
         clearstory]

Moby Thesaurus II by Grady Ward, 1.0:

23 Moby Thesaurus words for "clerestory":
   entresol, first floor, flat, floor, ground floor, level, mezzanine,
   mezzanine floor, rez-de-chaussee, ridgepole, roof, roofpole,
   rooftop, story, street floor, surface, top, top floor, top side,
   topside, topsides, upper side, upside