antenna

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. Zoology One of the paired, flexible, segmented sensory appendages on the head of an insect, myriapod, or crustacean functioning primarily as an organ of touch.
2. n. Something likened to this sensory appendage, as in function or form: sensitive public relations antennae.
3. n. A metallic apparatus for sending or receiving electromagnetic waves.

Century Dictionary and Cyclopedia

1. n. One of the lateral articulated appendages occurring in pairs on that segment of the head of an arthropod animal, as an insect, which immediately precedes the mouth or mandibular segment; a feeler or ‘horn.’ They vary greatly in size, shape, and function. The appendages of the head, proceeding forward from the mouth-parts, are: antennæ, antennulæ, ophthalmites or eye-stalks. plural In Crustacea: Properly, the posterior one of the two pairs of feelers or horns borne upon the head of most crustaceans, as crabs and lobsters, as distinguished from the anterior pair, or antennulæ. From their relative size they are known as the long feelers, in distinction from the antennulæ, or short feelers. When fully developed, the antennæ consist of a number of parts, which, beginning with the base, are named the basicerite, the scaphocerite, the ischiocerite, the merocerite, the carpocerite, and the (terminal) procerite. The last may consist of a long filament with many articulations, sometimes exceeding the whole length of the animal's body. See cuts under Cypris, Cythereidæ, and Limnetis. Loosely, either one of the two pairs of horns or feelers, that is, either the antennæ proper or the antennulæ. In Arachnida, or spiders, scorpions, etc., a chelicere; one of the pair of chelate or subchelate appendages of the head, situated between and morphologically in front of the large hooked or pincer-like appendages known as pedipalps. They are adapted for seizing and tearing, and sometimes convey a poisonduct. They are homologous with the feelers of crustaceans and insects, and are supposed, in some cases at least, to represent antennulæ as well as antennæ proper. See cuts under chelicera and scorpion. In Insecta and Myriapoda, a horn or feeler; one of the pair of jointed flexible sensitive appendages of the head, morphologically situated between the mouth-parts and the eyes, though generally appearing in the adult between or before the eyes. These characteristic organs are usually filamentous with many articulations, and are very diverse in form; some of the terms used in describing their shapes are filiform, denticulate, bipinnate, clavate, geniculate. In Coleoptera, divisions have been founded upon the shapes of the antennæ, as lamellicorn, clavicorn, longicorn, etc. These organs are almost universally present in some form or other, though occasionally rudimentary and inconspicuous, in which cases the insects are termed acerous, as distinguished from dicerous. The parts of a well-formed antenna usually recognized are the pedicel, scape, and flagellum or claveola, the last usually composing most of the length of the organ. See Hymenoptera, Insecta.
2. n. An analogous organ on the heads of other animals, as a feeler or tentacle, like the eye-stalk of a snail.
3. n. plural Projecting horns of iron or bronze found on some ancient helmets, perhaps serving only as ornaments, or as badges, or in some cases to stop a blow from glancing downward and striking the shoulder.
4. n. In Rotifera, a spur-like process bearing a tuft of setæ and projecting from the mid-dorsal line close to the trochal disk. Same as calcar, 4.
5. n. In electricity, the vertical conductor used in wireless telegraphy to send out electric waves (sender) or receive them (receiver).

Wiktionary

1. n. A feeler organ on the head of an insect, crab, or other animal.
2. n. An apparatus to receive or transmit radio waves and convert respectively to or from an electrical signal.
3. n. The faculty of intuitive astuteness.

GNU Webster's 1913

1. n. (Zoöl.) A movable, articulated organ of sensation, attached to the heads of insects and Crustacea. There are two in the former, and usually four in the latter. They are used as organs of touch, and in some species of Crustacea the cavity of the ear is situated near the basal joint. In insects, they are popularly called horns, and also feelers. The term in also applied to similar organs on the heads of other arthropods and of annelids.
2. n. (Electronics) A metallic device, variously shaped, designed for the purpose of either transmitting or receiving radio waves, as for radio or television broadcasting, or for transmitting communication signals. Some types are: whip antenna, antenna tower, horn antenna, dish antenna, directional antenna and rabbit ears. See transmitter, receiver.

WordNet 3.0

1. n. an electrical device that sends or receives radio or television signals
2. n. sensitivity similar to that of a receptor organ
3. n. one of a pair of mobile appendages on the head of e.g. insects and crustaceans; typically sensitive to touch and taste