Slaven

Etymology
Ultimately from, but, unlike the alternative forms, not directly inherited. The -a- vowel in the first syllable apparently derives from Russian Church Slavonic or, perhaps with influence from by folk etymology.

Proper noun

 * 1)  Slav
 * 2)  a man from Slavonia

Usage notes
Until the 18th century, the form of this word with -o- in the first syllable was almost universal throughout the Serbo-Croatian-speaking area (with varying reflexes of yat). The form with -a- seems to have originated in and spread under the influence of Pan-Slavism during the 19th century. By the 20th century, the form with -a- became the most common form in Croatia and all but disappeared from Serbia, effectively reversing the early 19th-century distribution of the two forms.