When you say something in the shortest, most direct way, you do it curtly. People who speak curtly tend to use as few words as possible.
Respond curtly to someone and you risk coming across as a bit rude, like when your sister asks for a bite of the brownie you're eating, and you curtly answer, "Nope." Or when a restaurant patron snaps at the server, curtly demanding a water refill. This adverb describes actions that are brief and to the point, and often brusque or abrupt. Curtly is derived from a root that means "to cut."