Wiktionary

1. Any of severalflightlesssea birds, oforderSphenisciformes, found in theSouthern Hemisphere; marked by their usual upright stance, walking on short legs, and (generally) their stark black and white plumage.
2. Anun.
3. A type of catch where the palm of the hand is facing towards the leg with the arm stretched downward, resembling the flipper of a penguin.
4. theTux penguin, the mascot ofLinux.

Century Dictionary and Cyclopedia

1. The wild pineapple,Bromelia Pinguin. Its ovoid succulent berry yields a cooling juice much used in fevers.
2. The great auk,Alca impennis; the original sense.
3. Any species of the familySpheniscidæ orAptenodytidæ. (SeeSpheniscidæ for technical characters.) Penguins are remarkably distinguished from all other birds by the reduction of the wings to mere flippers, covered with scaly feathers (seeImpennes, Squamipennes), used for swimming under water, but unfit for flight. The feathers of the upper parts have also broad flattened shafts and slight webs, being thus like scales; the feet are webbed and four-toed, though the hind toe is very short; the tail is short and stiff; the general form is stout and ungainly. On land the birds stand nearly erect and waddle clumsily, but they are agile and graceful in the water. They feed on fish and other animal food, and congregate on shore to breed in penguineries of great extent. Penguins are confined to the southern hemisphere, especially about Cape Horn and the Cape of Good Hope, and islands in high southern latitudes, coming nearest the equator on the west coast of South America, as in the case of Humboldt's penguin of Peru. There are more than a dozen species, referable to three leading types. Those of the genusAptenodytes are the largest, standing about three feet high, and have a slender bill. The namePatagonian penguin, applied to these, covers two species or varieties—a larger, the emperor penguin,A. forsteri orimperator, and a smaller,A. pennanti orrex. (Seeemperor.)Jackass-penguins, so called from braying, are medium-sized or rather small, with stout bill, asSpheniscus demersus of South Africa andS. magellanicus of Patagonia. (See cut atSpheniscus.) None of the foregoing are crested; but the members of the genusEudyptes (orCatarractes), asE. chrysocome orchrysolophus, known asrock-hoppers andmacaronis, have curly yellow plumes on each side of the head. (See cut atEudyptes.) Other medium-sized penguins arePygoscelis tæniata, P. antarctica, P. antipoda, andDasyrhamphus adeliæ. The smallest penguin, about a foot long, isEudyptila minor of Australian and New Zealand shores. The largest, which was taller than a man usually is, is a fossil species namedPalæeudyptes antarcticus, from the New Zealand Tertiary.

American Heritage® Dictionary of the English Language, Fourth Edition

1. Any of various stout flightless marine birds of the family Spheniscidae, of cool regions of the Southern Hemisphere, having flipperlike wings and webbed feet adapted for swimming and diving, and short scalelike feathers that are white in front and black on the back.
2. Obsolete The great auk.

1. Any bird of the order Impennes, or Ptilopteri. They are covered with short, thick feathers, almost scalelike on the wings, which are without true quills. They are unable to fly, but use their wings to aid in diving, in which they are very expert. See King penguin, underjackass.
2. The egg-shaped fleshy fruit of a West Indian plant (Bromelia Pinguin) of the Pineapple family; also, the plant itself, which has rigid, pointed, and spiny-toothed leaves, and is used for hedges.

WordNet 3.0

1. short-legged flightless birds of cold southern especially Antarctic regions having webbed feet and wings modified as flippers