ceiling

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The upper interior surface of a room.
• noun Material used to cover this surface.
• noun Something resembling a ceiling.
• noun An upper limit, especially as set by regulation.
• noun The highest altitude under particular weather conditions from which the ground is still visible.
• noun The altitude of the lowest layer of clouds.
• noun The maximum altitude that an aircraft can reach under a given set of conditions, such as a minimum rate of climb.
• noun Nautical The planking applied to the interior framework of a ship.

from The Century Dictionary.

• noun A canopy; hangings; properly, hangings overhead, but by extension also side-hangings; tapestry.
• noun The interior overhead surface of an apartment, usually formed of a lining of some kind affixed to the under side of joists supporting the floor above, or to rafters; the horizontal or curved surface of an interior, opposite the floor. In ordinary modern buildings it is usually finished with or formed of lath-and-plaster work.
• noun Wainscoting; wainscot.
• noun The lining of planks on the inside of a ship's frame.

from the GNU version of the Collaborative International Dictionary of English.

• noun The inside lining of a room overhead; the under side of the floor above; the upper surface opposite to the floor.
• noun The lining or finishing of any wall or other surface, with plaster, thin boards, etc.; also, the work when done.
• noun (Naut.) The inner planking of a vessel.
• noun See under Camp.
• noun Thin narrow boards used to ceil with.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun The surface that bounds the upper limit of a room.
• noun The upper limit of an object or action.
• noun aviation The highest altitude at which an aircraft may fly.
• noun mathematics The smallest integer greater than or equal to a given number.
• verb Present participle of ceil.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun maximum altitude at which a plane can fly (under specified conditions)
• noun (meteorology) altitude of the lowest layer of clouds
• noun an upper limit on what is allowed
• noun the overhead upper surface of a covered space