vienna

As a noun initialism

is a term formed from the initial letter or letters of several words or parts of words, but which is itself pronounced letter by letter.

As a proper noun vienna is

the capital of austria.

As a noun wiener

is a sausage made from beef, chicken or pork, also a hot dog.

As a proper noun Vienna is

the capital of Austria.

D is likely misspelled.

D has no English definition.

As a proper noun Vienna

is the capital of Austria.

As proper nouns the difference between bratislava and vienna

is that bratislava is the capital of slovakia while vienna is the capital of austria.