I was sure the word 'repeat' could be an adjective; for example, the phrase "repeat performance" describes a performance that is repeated. To my surprise, however, the Random House dictionary and World English Dictionary, don't have it in as an adjective, and nor does Wiktionary. So, is 'repeat' in "repeat performance" functioning as an adjective, or something else?
The Oxford English Dictionary also lists only the verb and the noun, but under the noun it has various compounds:
a. Forming compounds denoting a further example or instance of the specified noun, as repeat business, repeat order, repeat performance, etc.
b. Forming compounds denoting a person who does something (implied by the second element) again or repeatedly, as repeat customer, repeat offender, repeat viewer, repeat visitor, etc.
Linguists do not generally regard a modifier like "repeat" in "repeat performance" as an adjective, because it doesn't behave like an adjective in other ways (eg "*The performance was repeat", "*A very repeat performance", "*The repeatest performance")
Repeat is a noun, but it is used also as an attribute to mean "occurring, done, or used more than once," as in "a repeat prescription."