classified

Etymology 1

classify + -ed

verb

1. simple past and past participle of classify
   Make sure all the field observations are classified by species.

adj

1. Sorted into classes or categories.
2. Formally assigned by a government to one of several levels of sensitivity, usually (in English) top secret, secret, confidential, and, in some countries, restricted; thereby making disclosure to unauthorized persons illegal.
   We do not discuss specific interrogation techniques because they are classified information.
   Charlie: Where did you see this? Maverick: That's classified. I could tell you, but then I'd have to kill you. Charlie: I have Top Secret clearance. The Pentagon sees to it that I know more than you. 1986, Jim Cash, Jack Epps Jr., Top Gun (motion picture)
3. Not meant to be disclosed by a person or organization.
   I won't say who I'm going to the prom with; that's classified.

Etymology 2

From classified advertisement, by shortening.

noun

1. (informal) A classified advertisement in a newspaper or magazine.
   He ran a classified for the tools he wanted to sell.