Timbuktu

wiktionary

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Unclear. See Timbuktu § Toponymy.

etymonline

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Timbuktu

city on the southern edge of the Sahara desert, older spelling Timbuctoo, used allusively in English for "most distant place imaginable" from at least 1863. The name is from Songhai, literally "hollow," in reference to the depression in which it stands.