The Collaborative International Dictionary
Giaour \Giaour\, n. [Turk. giaur an infidel, Per. gawr, another
form of ghebr fire worshiper. Cf. Kaffir, Gheber .]
An infidel; -- a term applied by Turks to disbelievers in the
Mohammedan religion, especially Christrians.
--Byron.
Douglas Harper's Etymology Dictionary
1560s, Turkish term of contempt for non-Muslims, from Persian gaur, variant of gabr "fire-worshipper," originally applied to the adherents of the Zoroastrian religion.
Wiktionary
n. (context derogatory ethnic slur English) A non-Muslim, especially a Christian, an infidel; especially as used by Turkish people with particular reference to Christians such as Greeks, Armenians, Bulgarians, Serbs and Assyrians.
Wikipedia
Giaour or Gawur (; , , from gaur, ), meaning "infidel", is an offensive term, a slur, historically used in the Ottoman Empire for Christians, such as Orthodox Christians in the Balkans (non-Muslims). Christian ethnic groups in the Ottoman Empire referred to with the term include Greeks, Armenians, Bulgarians, Serbs and Assyrians among others. It was widely used in defters (tax registries) for Orthodox Christians.
The 1911 Encyclopædia Britannica described the term as follows:
Usage examples of "giaour".
On the same morning fresh bands set out from the Hospital Gate against the besieged monastery and against the big Turkish village of Kasteli, which the giaours had occupied.
Hospital Gate against the besieged monastery and against the big Turkish village of Kasteli, which the giaours had occupied.