tympanum

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. Anatomy See middle ear.
2. n. See eardrum.
3. n. Zoology A membranous external auditory structure, as in certain insects.
4. n. Architecture The ornamental recessed space or panel enclosed by the cornices of a triangular pediment.
5. n. Architecture A similar space between an arch and the lintel of a portal or window.
6. n. The diaphragm of a telephone.

Century Dictionary and Cyclopedia

1. n. An ancient tambourine or hand-drum, either with a single head like the modern tambourine, or with both front and back covered (the back sometimes swelled out as in a kettledrum), and beaten either with the hand or with a stick.
2. n. In anatomy and zoology: The ear-drum considered as to its walls, its cavity, and its contents. In man and other mammals the tympanum is the middle ear, a hollow or recess in the temporal bone, among several of the bones of which the temporal is composed, shut off from the meatus auditorius externus by the tympanic membrane, communicating with the back of the mouth by the Eustachian tube, in relation with the labyrinth, or inner ear, its inner wall forming part of the wall of the latter, and containing the chain of little bones called ossicula auditus, and usually the chorda tympani nerve. It is a part of the passageway which in the early embryo is uninterrupted between the pharynx and the exterior, and in the adult is occluded only by the membrane of the tympanum. In the dry state of the parts, the bony walls of the human tympanum present several openings: that leading outward through the external auditory meatus; the orifice of the Eustachian tube; the openings of mastoid cells; the fenestra ovalis and fenestra rotunda, respectively the terminations of the seala vestibuli and scala tympani, communicating with the vestibule and cochlea of the inner ear; the iter posterius, by which the chorda tympani nerve enters the tympanum from the aqueduct of Fallopius; the iter anterius, by which the same nerve leaves the tympanum by the canal of Huguier; the canal for the tensor tympani muscle; the Glaserian fissure, between the squamosal and the tympanic bones, for the laxator tympani muscle, tympanic artery, and slender process of the malleus, these last two openings being rifts between component bones of the parts communicating, like the Eustachian tube, with parts outside the temporal bone; and the minute orifice at the apex of the pyramid, for the passage of the stapedius muscle. In animals below mammals, as birds and reptiles, the tympanum contains the columella, when that bone exists, and is the cavity of the external ear when there is no external auditory meatus. Its membrane is often upon the surface of the head, and in some cases is a conspicuous structure of the exterior, as in a frog or toad. This is well shown in the cut under parotoid, where the circular formation just in front of the parotoid is the tympanum. See also cuts under ear and temporal.
3. n. The tympanic membrane; the ear-drum, in the restricted sense of that term: so used in physiology and aural surgery, and in common speech: as, a rupture of the tympanum. See tympanic membrane, under tympanic.
4. n. In ornithology: The labyrinth at the bottom of the windpipe of sundry birds, as the mergansers and various sea-ducks: a large irregular bony or gristly dilatation of the lower part of the trachea, often involving also more or less of the upper ends of the bronchi. It is chiefly found, or most developed, in the male sex.
5. n. The naked inflatable air-sac on each side of the neck of certain birds, as grouse, especially the sage-grouse and prairie-hen, in which the ordinary cervical air-cells of birds are inordinately developed and susceptible of great distention. See cut under Cupidonia.
6. n. In entomology, a tympanic membrane, stretched upon a chitinized ring, one surface being directed to the exterior, the other to the interior, in relation with a tracheal vesicle and with nervous ganglia and nervous end-organs in the form of clavate rods, as in the Orthoptera, where such an arrangement constitutes an auditory organ.
7. n. In architecture: The triangular space forming the field or back of a pediment, and included between the cornices of the inclined sides and the horizontal cornice; also, any space similarly marked off or bounded, as above a window, or between the lintel of a door and an arch above it. The tympanum often constitutes a field for sculpture in relief or in the round. See also cuts under pediment and pedimented.
8. n. The die or drum of a pedestal. See cuts under dado and pedestal.
9. n. The panel of a door.
10. n. In hydraul, engin., a water-raising current-wheel, originally made in the form of drum, whence the name. It is now a circular open-frame wheel, fitted with radial partitions so curved as to point upward on the rising side of the wheel and downward on the descending side. The wheel is suspended so that its lower edge is just submerged, and is turned by the current (or by other power), the partitions scooping up a quantity of water which, as the wheel revolves, runs hack to the axis of the wheel, where it is discharged; or it may discharge at some point of the periphery. While one of the most ancient forms of water-lifting machines, it is still used in drain age-works, though for small lifts it is now superseded by the scoop-wheel. E. H. Knight.
11. n. A kind of hollow tread-wheel wherein two or more persons walk in order to turn it, and thus give motion to a machine.
12. n. In botany, a membranous substance stretched across the theca. of a moss.

Wiktionary

1. n. architecture A triangular space between the sides of a pediment.
2. n. architecture The space within an arch, and above a lintel or a subordinate arch, spanning the opening below the arch.
3. n. The middle ear.
4. n. The eardrum.
5. n. A hearing organ in frogs, toads and some insects.
6. n. engineering A drum-shaped wheel with spirally curved partitions by which water is raised to the axis when the wheel revolves with the lower part of the circumference submerged; used for raising water, as for irrigation.

GNU Webster's 1913

1. n. The ear drum, or middle ear. Sometimes applied incorrectly to the tympanic membrane. See ear.
2. n. A chamber in the anterior part of the syrinx of birds.
3. n. (Zoöl.) One of the naked, inflatable air sacs on the neck of the prairie chicken and other species of grouse.
4. n. The recessed face of a pediment within the frame made by the upper and lower cornices, being usually a triangular space or table.
5. n. The space within an arch, and above a lintel or a subordinate arch, spanning the opening below the arch.
6. n. (Mech.) A drum-shaped wheel with spirally curved partitions by which water is raised to the axis when the wheel revolves with the lower part of the circumference submerged, -- used for raising water, as for irrigation.

WordNet 3.0

1. n. the membrane in the ear that vibrates to sound
2. n. the main cavity of the ear; between the eardrum and the inner ear
3. n. a large hemispherical brass or copper percussion instrument with a drumhead that can be tuned by adjusting the tension on it