History and naming
When Europeans first encountered turkeys in the Americas, they incorrectly identified the birds as a type of guineafowl (Numididae). Guineafowl were also known as turkey fowl (or turkey hen and turkey cock) because they were imported to Central Europe through Turkey. The name turkey fowl, shortened to just the name of the country, stuck as the name of the North American bird. In 1550, English navigator William Strickland, who had introduced the turkey into England, was granted a coat of arms including a "turkey-cock in his pride proper".
The confusion between these kinds of birds from related, but different, families is also reflected in the scientific name for the turkey genus: meleagris (μελεαγρίς) is Greek for guineafowl. Two major reasons why the name 'turkey fowl' stuck to Meleagris rather than to the Helmeted Guineafowl (Numida meleagris) were the genuine belief that the newly-discovered Americas were in fact a part of Asia, and the tendency during that time to attribute exotic animals and foods to a place that symbolized far-off, exotic lands.
In many countries, the name for turkeys refers to some other country. See List of names for the Wild Turkey.
Several other birds, which are sometimes called turkeys, are not particularly closely related: the Australian Brushturkey is a megapode, and the bird sometimes known as the "Australian Turkey" is the Australian Bustard, a gruiform. The bird sometimes called a Water Turkey is the Anhinga (Anhinga rufa), from the shape of its tail when the feathers are fully spread for drying.