UTHMAN EMPIRE

The word ottoman can refer to a type of footstool, a style of silk, or (with capitalization) to the former Turkish empire. Both items are, as you may expect, named after the caliphate: the stool became popular in European salons in the 1700s and was first recorded in French as ottomane due to an association with eastern European customs. The "silk" definition followed a similar route and was first used in the late nineteenth century. Ottoman eventually comes from the Arabic masculine proper name Uthman, for which I can't find a further etymology. You'll occasionally notice poets using Othman to refer to the people-group; this was both to be accurate in regard to the original Arabic form and for rhyming/metrical purposes. Surprisingly, usages of both capital- and lowercase-o Ottoman​ have been increasing lately.