On 24 July 1914, the Austro-Hungarian Ambassador to Serbia Baron Wladimir Giesl (pictured) sent a coded telegram to the Austro-Hungarian Minister of Foreign Affairs Leopold Count Berchtold. In his telegram, Giesl confirms what he means by the term “ultimatum”.
Baron von Giesl to Count Berchtold. Belgrade, 24 July 1914.
I only used the word “ultimatum” in my message to the Ministry of Foreign Affairs for shortness and simplicity.
Source: 1919 Austro-Hungarian Red Book, with minor edits.