Its species name is derived from Latin anatinus ('duck-like') from anas 'duck'. The scientific name Ornithorhynchus anatinus literally means 'duck-like bird-snout', deriving its genus name from the Greek root ornith- ( όρνιθ ornith or ὄρνις órnīs 'bird') and the word rhúnkhos ( ῥύγχος 'snout', 'beak'). Occasionally it is specifically called the 'duck-billed platypus'. Early British settlers called it by many names, such as 'watermole', 'duckbill', and 'duckmole'. Colloquially, the term 'platypi' is also used for the plural, although this is a form of pseudo-Latin going by the word's Greek roots the plural would be 'platypodes'. Scientists generally use 'platypuses' or simply 'platypus'. There is no universally-agreed plural form of 'platypus' in the English language. It was independently described as Ornithorhynchus paradoxus by Johann Blumenbach in 1800 (from a specimen given to him by Sir Joseph Banks) and following the rules of priority of nomenclature, it was later officially recognised as Ornithorhynchus anatinus. Shaw initially assigned the species the Linnaean name Platypus anatinus when he described it, but the genus term was quickly discovered to already be in use as the name of the wood-boring ambrosia beetle genus Platypus. The common name 'platypus' literally means 'flat-foot', deriving from the Greek word platúpous ( πλατύπους), from platús ( πλατύς 'broad, wide, flat') and poús ( πούς 'foot'). Shaw even took a pair of scissors to the dried skin to check for stitches.

It was thought that somebody had sewn a duck's beak onto the body of a beaver-like animal. George Shaw, who produced the first description of the animal in the Naturalist's Miscellany in 1799, stated it was impossible not to entertain doubts as to its genuine nature, and Robert Knox believed it might have been produced by some Asian taxidermist. British scientists' initial hunch was that the attributes were a hoax. When the platypus was first encountered by Europeans in 1798, a pelt and sketch were sent back to Great Britain by Captain John Hunter, the second Governor of New South Wales. See also: Plural form of words ending in -us Frederick Nodder's illustration from the first scientific description in 1799 of ' Platypus anatinus' It is classified as a near-threatened species by the IUCN, but a November 2020 report has recommended that it be upgraded to threatened species under the federal EPBC Act, due to habitat destruction and declining numbers in all states. Its population is not under severe threat, although captive-breeding programs have had slight success, and it is vulnerable to pollution. The platypus was hunted for its fur, but it has been a legally protected species in all states where it occurs since 1912.

It has appeared as a national mascot, features on the reverse of the Australian twenty-cent coin, and is an emblem of the state of New South Wales. It is culturally significant to several Aboriginal peoples, who also used to hunt it for food. The unique features of the platypus make it important in the study of evolutionary biology, and a recognisable and iconic symbol of Australia. In 1799, the first scientists to examine a preserved platypus body judged it a fake made of several animals sewn together. The unusual appearance of this egg-laying, duck-billed, beaver-tailed, otter-footed mammal at first baffled European naturalists. It is one of the few species of venomous mammals, as the male platypus has a spur on the hind foot that delivers an extremely painful venom. Like other monotremes, the platypus senses prey in cloudy water through electrolocation. Together with the four species of echidna, it is one of the five extant species of monotremes, mammals that lay eggs instead of giving birth to live young. The platypus is the sole living representative or monotypic taxon of its family Ornithorhynchidae and genus Ornithorhynchus, though a number of related species appear in the fossil record. The platypus ( Ornithorhynchus anatinus), sometimes referred to as the duck-billed platypus, is a semiaquatic, egg-laying mammal endemic to eastern Australia, including Tasmania.

Platypus baby licking moms milk