Here's an Adventures ruling question:
How do you pronounce "Duplicate?"
The majority of kingdom cards appear to be nouns. Some of these nouns can also be used as verbs, such as "Feast" or even "Count," but the clear implication is that most of the time the word is being used in the noun form. With most of these noun/verbs, the pronunciation is the same whether it's a noun or a verb, but "to duplicate" and "a duplicate" are pronounced differently. Is there an official ruling? Not that it makes any difference, but when playing IRL, you have to say the card name.
Then again, when describing your actions, it's not at all uncommon to use card names that are clearly nouns in place of verbs in a sentence. "I'm going to Throne Room a Smithy" is grammatically senseless outside of Dominion, but I'm guessing it's fairly common form.
P.S. Interestingly, while most kingdom cards are nouns, most events are verbs. Some of them are also noun/verbs, but most of those are probably intended to be verbs; I always think of "Ferry" as an action that I am taking, such as "I am going to Ferry Goons." This seems true for most events. Well...other than "Ball." Saying "I'm going to invite a couple of Duchesses to the Ball" just seems more polite than the alternative.