A uniquely addressable lockable box located on the premises of a post office that may be hired as collection point for mail. / (electricity) A test instrument once used by telephone engineers.

plural of post office box

plural of black-box function

(optimization) A function whose closed-form expression is not known or does not exist, and whose properties cannot be inferred.

The original form of boxing, in which no gloves were worn.

Someone who plays the cigar box guitar.

plural of cigar box guitarist

(music) A simple guitar-like string instrument that uses a cigar box as a resonator, and traditionally has a broomstick for a neck.

plural of cigar box guitar

(slang, dated, US) The USS Monitor, USS Montauk and similar American Civil War-era ironclad ships.