Slovak, Slavic, Slavonic...
Q: What's the difference?
The Slavs were a people who spoke the Ancient Slavic language about 2,000 years ago. They probably lived north-east of today's Slovakia, some suggest they may have been in Central Europe too. Slovak archeologists and historians assume that they began to reach present-day Slovakia's territory sometime after 500 CE, and that by about 600 CE at the latest, some were already there.
The ancient language has since separated into a number of languages that include Slovak, Polish, Rusyn, Croatian, Russian – over a dozen altogether. Each of them is a Slavic language. They belong to the family of Slavic languages, because they have Ancient Slavic as their common ancestor.
British English uses the word Slavonic instead, Slavic and Slavonic mean the same. Slovak is a Slavic or a Slavonic language. (See table at bottom.)
Switch to country names
The Slavs had populated a large part of Central Europe and many other areas by around 800 CE. As countries began to emerge around them, many adopted the name of the country as their own: the Slavs who found themselves in the Kingdom of Poland began to call themselves Poles, the Slavs in the Margraviate of Moravia called themselves Moravians, etc.
Kingdom of Hungary
Some Slavs were incorporated in countries whose names were already linked to speakers of non-Slavic languages. Those Slavs were able to retain their original name, because it distinguished them from the other people in their own country and soon also from the Slavs in the neighboring countries who replaced their original name with a country designation.
That was the case with the Slovaks in the Kingdom of Hungary, with the Slovenes, who were incorporated in the expanding German-Austrian realm, and a few other groups whose languages have since disappeared. As the Slovaks' (and Slovenes') word for themselves and the Slavs underwent historical changes, it ceased to refer to all the Slavs and came to mean only them. That is why the words are similar. They also developed a new word in the general meaning of "Slav."
Slavish, Slovac, Slavack...
As long ago as in 1845 a letter to a U.S. newspaper clarified the difference between on the one hand speaking specifically about the Slovaks and on the other hand about the Slavs (Slaviane, as the author called them) in a general sense:

But when the immigrants used English in the 19th and early 20th centuries, they were often as uncertain of the English versions of their ethnic names as the Americans were confounded by the similarity. In addition to calling their fraternals and parishes Slovak, some Slovak-Americans would name them Slovac and Slavish. The word Slovak had generally replaced other versions in the names of Slovak-American organizations by the mid-1920s. Although not as common in Slovak-American documents, English-language sources also used Slavack, Slovish, and similar words. Context is usually required to clarify whether the reference was to the Slovaks, Slavs, or Slovenes.
| Country | Language | Person | Adjective | Note |
| Slovakia | Slovak | Slovak | Slovak (Slovakian) |
-ian is not used by official Slovak sources. |
| Slovenia | Slovene or Slovenian | Slovene or Slovenian | Slovene or Slovenian | Both used officially. |
| – | Slavic (or Slavonic) |
Slav | Slavic (or Slavonic) |
Historical or modern language family. |
| – | Church Slavic (or Slavonic) |
– | Church Slavic (or Slavonic) |
Byzantine and Orthodox religious language. |
| – | Old Church Slavic (or Slavonic) |
– | Old Church Slavic (or Slavonic) |
Slavs' religious language from 863 CE |
| – | Old Slavic or Ancient Slavic (Slavonic) |
Old Slav or Ancient Slav |
Old Slavic or Ancient Slavic (Slavonic) |
Sometimes used about Slavs before ca. 900 CE |
| Slavonia | – | (Slavonian) | Slavonian | Territory in Croatia. |
| (Slovincian) | Extinct. |



