What is the compound adjective in the sentence she ordered a ham sandwich in sourdough bread?

The compound adjective in the sentence "She ordered a ham sandwich in sourdough bread" is "sourdough." It describes the type of bread used for the sandwich, indicating that the bread is made through the sourdough fermentation process. While "ham" is also an adjective describing the sandwich, "sourdough" specifically combines with "bread" to form a compound adjective.