Ottoman Turkish (Ottoman Turkish: لِسانِ عُثمانى, romanized: Lisân-ı Osmânî, Turkish pronunciation: [li'saːnɯ os'maːniː]; Turkish: Osmanlı Türkçesi) was the standardized register of the Turkish language used by the citizens of the Ottoman Empire (14th to 20th centuries CE). It borrowed extensively, in all aspects, from Arabic and Persian, and its speakers used the Ottoman Turkish alphabet for written communication. During the peak of Ottoman power (c. 16th century CE), words of foreign origin in Turkish literature in the Ottoman Empire heavily outnumbered native Turkish words, with Arabic and Persian vocabulary accounting for up to 88% of the Ottoman vocabulary in some texts.

Consequently, Ottoman Turkish was largely unintelligible to the less-educated lower-class and to rural Turks, who continued to use kaba Türkçe ("raw/vulgar Turkish"; compare Vulgar Latin and Demotic Greek), which used far fewer foreign loanwords and is the basis of the modern standard. The Tanzimât era (1839–1876) saw the application of the term "Ottoman" when referring to the language (لسان عثمانی lisân-ı Osmânî or عثمانليجه Osmanlıca); Modern Turkish uses the same terms when referring to the language of that era (Osmanlıca and Osmanlı Türkçesi). More generically, the Turkish language was called تركچه Türkçe or تركی Türkî "Turkish".