hollow

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

• adjective Having a cavity, gap, or space within.
• adjective Deeply indented or concave; sunken.
• adjective Without substance or character: synonym: vain.
• adjective Devoid of truth or validity; specious.
• adjective Having a reverberating, sepulchral sound.
• noun A cavity, gap, or space.
• noun An indented or concave surface or area.
• noun A void; an emptiness.
• noun A small valley between hills or mountains.
• intransitive verb To make hollow.
• intransitive verb To scoop or form by making concave.
• intransitive verb To become hollow or empty.

from The Century Dictionary.

• noun A cavity; a depression or an excavation below the general level, as of the ground, or in the substance of anything; an empty space in anything; a concavity.
• noun Specifically, a concave space of ground; a piece or tract of land lower than the general level, or hemmed in by hills: used in many place-names in the United States: as, Sleepy Hollow in New York.
• noun A concave plane used in working moldings.
• noun A strip of thick paper or of pasteboard cut to the exact height and thickness required for a book for which the boards and cloth are intended, and which acts as a gage for the guidance of the case-makers, and as a stiffener for the cloth at the back of the book between the boards.
• Having a cavity within; having an empty space in the interior: as, a hollow tree; a hollow rock; a hollow sphere.
• Having a concavity; concave; sunken: as, a hollow way or road.
• Resembling sound reverberated from a cavity, or producing such a sound; deep; low.
• Empty; without contents; hence, without pith or substance; fruitless; worthless: as, a hollow victory; a hollow argument.
• Not sincere or faithful; false; deceitful; not sound: as, a hollow heart.
• Void of meaning or truth; empty; baseless: as, hollow oaths; a hollow mockery.
• Thorough; complete; out-and-out.
• Having, as wool, the fibers torn apart, so that it is light and open.
• Synonyms Empty, void, cavernous.
• Faithless, iusincere, treacherous, hypocritical.
• To make hollow; excavate; make empty.
• To bend into a curved or concave form.
• Beyond doubt or question; utterly; completely; out-and-out: often with all for emphasis: as, he beat him hollow, or all hollow; he carried it hollow.
• A variant of hollo.

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

• transitive verb To urge or call by shouting.
• transitive verb To make hollow, as by digging, cutting, or engraving; to excavate.
• noun A cavity, natural or artificial; an unfilled space within anything; a hole, a cavern; an excavation; as the hollow of the hand or of a tree.
• noun A low spot surrounded by elevations; a depressed part of a surface; a concavity; a channel.
• adjective Having an empty space or cavity, natural or artificial, within a solid substance; not solid; excavated in the interior
• adjective Depressed; concave; gaunt; sunken.
• adjective Reverberated from a cavity, or resembling such a sound; deep; muffled.
• adjective Not sincere or faithful; false; deceitful; not sound
• adjective (Arch.) an opening in the center of a winding staircase in place of a newel post, the stairs being supported by the wall; an open newel; also, the stringpiece or rail winding around the well of such a staircase.
• adjective (Engin.) a pier of stone or brick made behind the lock gates of a canal, and containing a hollow or recess to receive the ends of the gates.
• adjective (Bot.) See Moschatel.
• adjective See Square.
• adjective hollow vessels; -- a trade name for cast-iron kitchen utensils, earthenware, etc.
• interjection Hollo.
• adverb colloq. Wholly; completely; utterly; -- chiefly after the verb to beat, and often with all. See all, adv.
• intransitive verb To shout; to hollo.

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

• verb To urge or call by shouting; to hollo.
• noun A small valley between mountains; "he built himself a cabin in a hollow high up in the Rockies"
• noun A sunken area in something solid.
• noun US A sunken area, the equivalent to a copse in British English.