A word or phrase that appears throughout an Arc as a Motif.
Arc Words can be a way to hint at the Aesop or one of the themes of a show, often in the form of a question the characters must find an answer to. Alternately, they can be used for Foreshadowing.
They're often cryptic, and left unexplained until The Climax or Dénouement. This builds up tension and mystery, and hints that anyone using the words knows more than they're telling. This enigmatic variant is a typical element of a Mind Screw, and is sometimes used as a memetic way of advertising the show.
Arc Words need not have attention drawn explicitly to them; they often rely instead on eagle-eyed/sharp eared viewers noticing for themselves. In the "Bad Wolf" example from the first series of the revival of Doctor Who, the words appeared as, among other things, a helicopter's callsign, a reference in dialogue to "The Big Bad Wolf", a graffito, and even in other languages (the [inaccurate] German Schlechter Wolf, and the Welsh Blaidd Drwg, the latter tipping off the Doctor about it).
Look for these on the Internet Movie Database "memorable quotes" page for the show, with the label "repeated line".
Arc Words has been suggested to play 7 roles. Click below to see other actors suggested for each role, and vote for who you think would play the role best.