n. 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.n. 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.n. A concave plane used in working moldings.n. 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.