The Collaborative International Dictionary of English v.0.48:

Ceil \Ceil\ (s[=e]l), v. t. [imp. & p. p. Ceiled (s[=e]ld); p.
   pr. & vb. n. Ceiling.] [From an older noun, fr. F. ciel
   heaven, canopy, fr. L. caelum heaven, vault, arch, covering;
   cf. Gr. koi^los hollow.]
   1. To overlay or cover the inner side of the roof of; to
      furnish with a ceiling; as, to ceil a room.
      [1913 Webster]

            The greater house he ceiled with fir tree. --2
                                                  Chron. iii. 5
      [1913 Webster]

   2. To line or finish a surface, as of a wall, with plaster,
      stucco, thin boards, or the like.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Ceiling \Ceil"ing\, n. [See Cell, v. t.]
   1. (Arch.)
      (a) The inside lining of a room overhead; the under side
          of the floor above; the upper surface opposite to the
          floor.
      (b) The lining or finishing of any wall or other surface,
          with plaster, thin boards, etc.; also, the work when
          done.
          [1913 Webster]

   2. (Naut.) The inner planking of a vessel.
      [1913 Webster]

   Camp ceiling. See under Camp.

   Ceiling boards, Thin narrow boards used to ceil with.
      [1913 Webster]

WordNet (r) 3.0 (2006):

ceiling
    n 1: the overhead upper surface of a covered space; "he hated
         painting the ceiling"
    2: (meteorology) altitude of the lowest layer of clouds
    3: an upper limit on what is allowed; "he put a ceiling on the
       number of women who worked for him"; "there was a roof on
       salaries"; "they established a cap for prices" [syn:
       ceiling, roof, cap]
    4: maximum altitude at which a plane can fly (under specified
       conditions)